spring-security/docs/modules/ROOT/pages/reactive/oauth2/client/authorization-grants.adoc

[[oauth2Client-auth-grant-support]]
= Authorization Grant Support


[[oauth2Client-auth-code-grant]]
== Authorization Code

[NOTE]
Please refer to the OAuth 2.0 Authorization Framework for further details on the https://tools.ietf.org/html/rfc6749#section-1.3.1[Authorization Code] grant.


=== Obtaining Authorization

[NOTE]
Please refer to the https://tools.ietf.org/html/rfc6749#section-4.1.1[Authorization Request/Response] protocol flow for the Authorization Code grant.


=== Initiating the Authorization Request

The `OAuth2AuthorizationRequestRedirectWebFilter` uses a `ServerOAuth2AuthorizationRequestResolver` to resolve an `OAuth2AuthorizationRequest` and initiate the Authorization Code grant flow by redirecting the end-user's user-agent to the Authorization Server's Authorization Endpoint.

The primary role of the `ServerOAuth2AuthorizationRequestResolver` is to resolve an `OAuth2AuthorizationRequest` from the provided web request.
The default implementation `DefaultServerOAuth2AuthorizationRequestResolver` matches on the (default) path `+/oauth2/authorization/{registrationId}+` extracting the `registrationId` and using it to build the `OAuth2AuthorizationRequest` for the associated `ClientRegistration`.

Given the following Spring Boot properties for an OAuth 2.0 Client registration:

[source,yaml,attrs="-attributes"]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-secret: okta-client-secret
            authorization-grant-type: authorization_code
            redirect-uri: "{baseUrl}/authorized/okta"
            scope: read, write
        provider:
          okta:
            authorization-uri: https://dev-1234.oktapreview.com/oauth2/v1/authorize
            token-uri: https://dev-1234.oktapreview.com/oauth2/v1/token
----

A request with the base path `/oauth2/authorization/okta` will initiate the Authorization Request redirect by the `OAuth2AuthorizationRequestRedirectWebFilter` and ultimately start the Authorization Code grant flow.

[NOTE]
The `AuthorizationCodeReactiveOAuth2AuthorizedClientProvider` is an implementation of `ReactiveOAuth2AuthorizedClientProvider` for the Authorization Code grant,
which also initiates the Authorization Request redirect by the `OAuth2AuthorizationRequestRedirectWebFilter`.

If the OAuth 2.0 Client is a https://tools.ietf.org/html/rfc6749#section-2.1[Public Client], then configure the OAuth 2.0 Client registration as follows:

[source,yaml,attrs="-attributes"]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-authentication-method: none
            authorization-grant-type: authorization_code
            redirect-uri: "{baseUrl}/authorized/okta"
            ...
----

Public Clients are supported using https://tools.ietf.org/html/rfc7636[Proof Key for Code Exchange] (PKCE).
If the client is running in an untrusted environment (eg. native application or web browser-based application) and therefore incapable of maintaining the confidentiality of it's credentials, PKCE will automatically be used when the following conditions are true:

. `client-secret` is omitted (or empty)
. `client-authentication-method` is set to "none" (`ClientAuthenticationMethod.NONE`)

[TIP]
If the OAuth 2.0 Provider supports PKCE for https://tools.ietf.org/html/rfc6749#section-2.1[Confidential Clients], you may (optionally) configure it using `DefaultServerOAuth2AuthorizationRequestResolver.setAuthorizationRequestCustomizer(OAuth2AuthorizationRequestCustomizers.withPkce())`.

[[oauth2Client-auth-code-redirect-uri]]
The `DefaultServerOAuth2AuthorizationRequestResolver` also supports `URI` template variables for the `redirect-uri` using `UriComponentsBuilder`.

The following configuration uses all the supported `URI` template variables:

[source,yaml,attrs="-attributes"]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            ...
            redirect-uri: "{baseScheme}://{baseHost}{basePort}{basePath}/authorized/{registrationId}"
            ...
----

[NOTE]
`+{baseUrl}+` resolves to `+{baseScheme}://{baseHost}{basePort}{basePath}+`

Configuring the `redirect-uri` with `URI` template variables is especially useful when the OAuth 2.0 Client is running behind a xref:features/exploits/http.adoc#http-proxy-server[Proxy Server].
This ensures that the `X-Forwarded-*` headers are used when expanding the `redirect-uri`.

=== Customizing the Authorization Request

One of the primary use cases a `ServerOAuth2AuthorizationRequestResolver` can realize is the ability to customize the Authorization Request with additional parameters above the standard parameters defined in the OAuth 2.0 Authorization Framework.

For example, OpenID Connect defines additional OAuth 2.0 request parameters for the https://openid.net/specs/openid-connect-core-1_0.html#AuthRequest[Authorization Code Flow] extending from the standard parameters defined in the https://tools.ietf.org/html/rfc6749#section-4.1.1[OAuth 2.0 Authorization Framework].
One of those extended parameters is the `prompt` parameter.

[NOTE]
====
The `prompt` parameter is optional. Space delimited, case sensitive list of ASCII string values that specifies whether the Authorization Server prompts the End-User for re-authentication and consent. The defined values are: `none`, `login`, `consent`, and `select_account`.
====

The following example shows how to configure the `DefaultServerOAuth2AuthorizationRequestResolver` with a `Consumer<OAuth2AuthorizationRequest.Builder>` that customizes the Authorization Request for `oauth2Login()`, by including the request parameter `prompt=consent`.

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Configuration
@EnableWebFluxSecurity
public class OAuth2LoginSecurityConfig {

	@Autowired
	private ReactiveClientRegistrationRepository clientRegistrationRepository;

	@Bean
	public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
		http
			.authorizeExchange(authorize -> authorize
				.anyExchange().authenticated()
			)
			.oauth2Login(oauth2 -> oauth2
				.authorizationRequestResolver(
					authorizationRequestResolver(this.clientRegistrationRepository)
				)
			);
		return http.build();
	}

	private ServerOAuth2AuthorizationRequestResolver authorizationRequestResolver(
			ReactiveClientRegistrationRepository clientRegistrationRepository) {

		DefaultServerOAuth2AuthorizationRequestResolver authorizationRequestResolver =
				new DefaultServerOAuth2AuthorizationRequestResolver(
						clientRegistrationRepository);
		authorizationRequestResolver.setAuthorizationRequestCustomizer(
				authorizationRequestCustomizer());

		return  authorizationRequestResolver;
	}

	private Consumer<OAuth2AuthorizationRequest.Builder> authorizationRequestCustomizer() {
		return customizer -> customizer
					.additionalParameters(params -> params.put("prompt", "consent"));
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Configuration
@EnableWebFluxSecurity
class SecurityConfig {

    @Autowired
    private lateinit var customClientRegistrationRepository: ReactiveClientRegistrationRepository

    @Bean
    fun securityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
        http {
            authorizeExchange {
                authorize(anyExchange, authenticated)
            }
            oauth2Login {
                authorizationRequestResolver = authorizationRequestResolver(customClientRegistrationRepository)
            }
        }

        return http.build()
    }

    private fun authorizationRequestResolver(
            clientRegistrationRepository: ReactiveClientRegistrationRepository): ServerOAuth2AuthorizationRequestResolver {
        val authorizationRequestResolver = DefaultServerOAuth2AuthorizationRequestResolver(
                clientRegistrationRepository)
        authorizationRequestResolver.setAuthorizationRequestCustomizer(
                authorizationRequestCustomizer())
        return authorizationRequestResolver
    }

    private fun authorizationRequestCustomizer(): Consumer<OAuth2AuthorizationRequest.Builder> {
        return Consumer { customizer ->
            customizer
                .additionalParameters { params -> params["prompt"] = "consent" }
        }
    }
}
----
======

For the simple use case, where the additional request parameter is always the same for a specific provider, it may be added directly in the `authorization-uri` property.

For example, if the value for the request parameter `prompt` is always `consent` for the provider `okta`, than simply configure as follows:

[source,yaml]
----
spring:
  security:
    oauth2:
      client:
        provider:
          okta:
            authorization-uri: https://dev-1234.oktapreview.com/oauth2/v1/authorize?prompt=consent
----

The preceding example shows the common use case of adding a custom parameter on top of the standard parameters.
Alternatively, if your requirements are more advanced, you can take full control in building the Authorization Request URI by simply overriding the `OAuth2AuthorizationRequest.authorizationRequestUri` property.

[TIP]
`OAuth2AuthorizationRequest.Builder.build()` constructs the `OAuth2AuthorizationRequest.authorizationRequestUri`, which represents the Authorization Request URI including all query parameters using the `application/x-www-form-urlencoded` format.

The following example shows a variation of `authorizationRequestCustomizer()` from the preceding example, and instead overrides the `OAuth2AuthorizationRequest.authorizationRequestUri` property.

[tabs]
======
Java::
+
[source,java,role="primary"]
----
private Consumer<OAuth2AuthorizationRequest.Builder> authorizationRequestCustomizer() {
	return customizer -> customizer
			.authorizationRequestUri(uriBuilder -> uriBuilder
					.queryParam("prompt", "consent").build());
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
private fun authorizationRequestCustomizer(): Consumer<OAuth2AuthorizationRequest.Builder> {
    return Consumer { customizer: OAuth2AuthorizationRequest.Builder ->
        customizer
                .authorizationRequestUri { uriBuilder: UriBuilder ->
                    uriBuilder
                            .queryParam("prompt", "consent").build()
                }
    }
}
----
======


=== Storing the Authorization Request

The `ServerAuthorizationRequestRepository` is responsible for the persistence of the `OAuth2AuthorizationRequest` from the time the Authorization Request is initiated to the time the Authorization Response is received (the callback).

[TIP]
The `OAuth2AuthorizationRequest` is used to correlate and validate the Authorization Response.

The default implementation of `ServerAuthorizationRequestRepository` is `WebSessionOAuth2ServerAuthorizationRequestRepository`, which stores the `OAuth2AuthorizationRequest` in the `WebSession`.

If you have a custom implementation of `ServerAuthorizationRequestRepository`, you may configure it as shown in the following example:

.ServerAuthorizationRequestRepository Configuration
[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Configuration
@EnableWebFluxSecurity
public class OAuth2ClientSecurityConfig {

	@Bean
	public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
		http
			.oauth2Client(oauth2 -> oauth2
				.authorizationRequestRepository(this.authorizationRequestRepository())
				...
			);
		return http.build();
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Configuration
@EnableWebFluxSecurity
class OAuth2ClientSecurityConfig {

    @Bean
    fun securityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
        http {
            oauth2Client {
                authorizationRequestRepository = authorizationRequestRepository()
            }
        }

        return http.build()
    }
}
----
======

=== Requesting an Access Token

[NOTE]
Please refer to the https://tools.ietf.org/html/rfc6749#section-4.1.3[Access Token Request/Response] protocol flow for the Authorization Code grant.

The default implementation of `ReactiveOAuth2AccessTokenResponseClient` for the Authorization Code grant is `WebClientReactiveAuthorizationCodeTokenResponseClient`, which uses a `WebClient` for exchanging an authorization code for an access token at the Authorization Server’s Token Endpoint.

The `WebClientReactiveAuthorizationCodeTokenResponseClient` is quite flexible as it allows you to customize the pre-processing of the Token Request and/or post-handling of the Token Response.


=== Customizing the Access Token Request

If you need to customize the pre-processing of the Token Request, you can provide `WebClientReactiveAuthorizationCodeTokenResponseClient.setParametersConverter()` with a custom `Converter<OAuth2AuthorizationCodeGrantRequest, MultiValueMap<String, String>>`.
The default implementation builds a `MultiValueMap<String, String>` containing only the `grant_type` parameter of a standard https://tools.ietf.org/html/rfc6749#section-4.1.3[OAuth 2.0 Access Token Request] which is used to construct the request. Other parameters required by the Authorization Code grant are added directly to the body of the request by the `WebClientReactiveAuthorizationCodeTokenResponseClient`.
However, providing a custom `Converter`, would allow you to extend the standard Token Request and add custom parameter(s).

[TIP]
If you prefer to only add additional parameters, you can instead provide `WebClientReactiveAuthorizationCodeTokenResponseClient.addParametersConverter()` with a custom `Converter<OAuth2AuthorizationCodeGrantRequest, MultiValueMap<String, String>>` which constructs an aggregate `Converter`.

IMPORTANT: The custom `Converter` must return valid parameters of an OAuth 2.0 Access Token Request that is understood by the intended OAuth 2.0 Provider.


=== Customizing the Access Token Response

On the other end, if you need to customize the post-handling of the Token Response, you will need to provide `WebClientReactiveAuthorizationCodeTokenResponseClient.setBodyExtractor()` with a custom configured `BodyExtractor<Mono<OAuth2AccessTokenResponse>, ReactiveHttpInputMessage>` that is used for converting the OAuth 2.0 Access Token Response to an `OAuth2AccessTokenResponse`.
The default implementation provided by `OAuth2BodyExtractors.oauth2AccessTokenResponse()` parses the response and handles errors accordingly.

=== Customizing the `WebClient`

Alternatively, if your requirements are more advanced, you can take full control of the request/response by simply providing `WebClientReactiveAuthorizationCodeTokenResponseClient.setWebClient()` with a custom configured `WebClient`.

Whether you customize `WebClientReactiveAuthorizationCodeTokenResponseClient` or provide your own implementation of `ReactiveOAuth2AccessTokenResponseClient`, you’ll need to configure it as shown in the following example:

.Access Token Response Configuration
[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Configuration
@EnableWebFluxSecurity
public class OAuth2ClientSecurityConfig {

	@Bean
	public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
		http
			.oauth2Client(oauth2 -> oauth2
				.authenticationManager(this.authorizationCodeAuthenticationManager())
				...
			);
		return http.build();
	}

	private ReactiveAuthenticationManager authorizationCodeAuthenticationManager() {
		WebClientReactiveAuthorizationCodeTokenResponseClient accessTokenResponseClient =
				new WebClientReactiveAuthorizationCodeTokenResponseClient();
		...

		return new OAuth2AuthorizationCodeReactiveAuthenticationManager(accessTokenResponseClient);
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Configuration
@EnableWebFluxSecurity
class OAuth2ClientSecurityConfig {

    @Bean
    fun securityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
        http {
            oauth2Client {
                authenticationManager = authorizationCodeAuthenticationManager()
            }
        }

        return http.build()
    }

    private fun authorizationCodeAuthenticationManager(): ReactiveAuthenticationManager {
        val accessTokenResponseClient = WebClientReactiveAuthorizationCodeTokenResponseClient()
        ...

        return OAuth2AuthorizationCodeReactiveAuthenticationManager(accessTokenResponseClient)
    }
}
----
======


[[oauth2Client-refresh-token-grant]]
== Refresh Token

[NOTE]
Please refer to the OAuth 2.0 Authorization Framework for further details on the https://tools.ietf.org/html/rfc6749#section-1.5[Refresh Token].


=== Refreshing an Access Token

[NOTE]
Please refer to the https://tools.ietf.org/html/rfc6749#section-6[Access Token Request/Response] protocol flow for the Refresh Token grant.

The default implementation of `ReactiveOAuth2AccessTokenResponseClient` for the Refresh Token grant is `WebClientReactiveRefreshTokenTokenResponseClient`, which uses a `WebClient` when refreshing an access token at the Authorization Server’s Token Endpoint.

The `WebClientReactiveRefreshTokenTokenResponseClient` is quite flexible as it allows you to customize the pre-processing of the Token Request and/or post-handling of the Token Response.


=== Customizing the Access Token Request

If you need to customize the pre-processing of the Token Request, you can provide `WebClientReactiveRefreshTokenTokenResponseClient.setParametersConverter()` with a custom `Converter<OAuth2RefreshTokenGrantRequest, MultiValueMap<String, String>>`.
The default implementation builds a `MultiValueMap<String, String>` containing only the `grant_type` parameter of a standard https://tools.ietf.org/html/rfc6749#section-6[OAuth 2.0 Access Token Request] which is used to construct the request. Other parameters required by the Refresh Token grant are added directly to the body of the request by the `WebClientReactiveRefreshTokenTokenResponseClient`.
However, providing a custom `Converter`, would allow you to extend the standard Token Request and add custom parameter(s).

[TIP]
If you prefer to only add additional parameters, you can instead provide `WebClientReactiveRefreshTokenTokenResponseClient.addParametersConverter()` with a custom `Converter<OAuth2RefreshTokenGrantRequest, MultiValueMap<String, String>>` which constructs an aggregate `Converter`.

IMPORTANT: The custom `Converter` must return valid parameters of an OAuth 2.0 Access Token Request that is understood by the intended OAuth 2.0 Provider.


=== Customizing the Access Token Response

On the other end, if you need to customize the post-handling of the Token Response, you will need to provide `WebClientReactiveRefreshTokenTokenResponseClient.setBodyExtractor()` with a custom configured `BodyExtractor<Mono<OAuth2AccessTokenResponse>, ReactiveHttpInputMessage>` that is used for converting the OAuth 2.0 Access Token Response to an `OAuth2AccessTokenResponse`.
The default implementation provided by `OAuth2BodyExtractors.oauth2AccessTokenResponse()` parses the response and handles errors accordingly.

=== Customizing the `WebClient`

Alternatively, if your requirements are more advanced, you can take full control of the request/response by simply providing `WebClientReactiveRefreshTokenTokenResponseClient.setWebClient()` with a custom configured `WebClient`.

Whether you customize `WebClientReactiveRefreshTokenTokenResponseClient` or provide your own implementation of `ReactiveOAuth2AccessTokenResponseClient`, you’ll need to configure it as shown in the following example:

.Access Token Response Configuration
[tabs]
======
Java::
+
[source,java,role="primary"]
----
// Customize
ReactiveOAuth2AccessTokenResponseClient<OAuth2RefreshTokenGrantRequest> refreshTokenTokenResponseClient = ...

ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
		ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
				.authorizationCode()
				.refreshToken(configurer -> configurer.accessTokenResponseClient(refreshTokenTokenResponseClient))
				.build();

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
// Customize
val refreshTokenTokenResponseClient: ReactiveOAuth2AccessTokenResponseClient<OAuth2RefreshTokenGrantRequest> = ...

val authorizedClientProvider: ReactiveOAuth2AuthorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
        .authorizationCode()
        .refreshToken { it.accessTokenResponseClient(refreshTokenTokenResponseClient) }
        .build()

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
----
======

[NOTE]
`ReactiveOAuth2AuthorizedClientProviderBuilder.builder().refreshToken()` configures a `RefreshTokenReactiveOAuth2AuthorizedClientProvider`,
which is an implementation of a `ReactiveOAuth2AuthorizedClientProvider` for the Refresh Token grant.

The `OAuth2RefreshToken` may optionally be returned in the Access Token Response for the `authorization_code` and `password` grant types.
If the `OAuth2AuthorizedClient.getRefreshToken()` is available and the `OAuth2AuthorizedClient.getAccessToken()` is expired, it will automatically be refreshed by the `RefreshTokenReactiveOAuth2AuthorizedClientProvider`.


[[oauth2Client-client-creds-grant]]
== Client Credentials

[NOTE]
Please refer to the OAuth 2.0 Authorization Framework for further details on the https://tools.ietf.org/html/rfc6749#section-1.3.4[Client Credentials] grant.


=== Requesting an Access Token

[NOTE]
Please refer to the https://tools.ietf.org/html/rfc6749#section-4.4.2[Access Token Request/Response] protocol flow for the Client Credentials grant.

The default implementation of `ReactiveOAuth2AccessTokenResponseClient` for the Client Credentials grant is `WebClientReactiveClientCredentialsTokenResponseClient`, which uses a `WebClient` when requesting an access token at the Authorization Server’s Token Endpoint.

The `WebClientReactiveClientCredentialsTokenResponseClient` is quite flexible as it allows you to customize the pre-processing of the Token Request and/or post-handling of the Token Response.


=== Customizing the Access Token Request

If you need to customize the pre-processing of the Token Request, you can provide `WebClientReactiveClientCredentialsTokenResponseClient.setParametersConverter()` with a custom `Converter<OAuth2ClientCredentialsGrantRequest, MultiValueMap<String, String>>`.
The default implementation builds a `MultiValueMap<String, String>` containing only the `grant_type` parameter of a standard https://tools.ietf.org/html/rfc6749#section-4.4.2[OAuth 2.0 Access Token Request] which is used to construct the request. Other parameters required by the Client Credentials grant are added directly to the body of the request by the `WebClientReactiveClientCredentialsTokenResponseClient`.
However, providing a custom `Converter`, would allow you to extend the standard Token Request and add custom parameter(s).

[TIP]
If you prefer to only add additional parameters, you can instead provide `WebClientReactiveClientCredentialsTokenResponseClient.addParametersConverter()` with a custom `Converter<OAuth2ClientCredentialsGrantRequest, MultiValueMap<String, String>>` which constructs an aggregate `Converter`.

IMPORTANT: The custom `Converter` must return valid parameters of an OAuth 2.0 Access Token Request that is understood by the intended OAuth 2.0 Provider.


=== Customizing the Access Token Response

On the other end, if you need to customize the post-handling of the Token Response, you will need to provide `WebClientReactiveClientCredentialsTokenResponseClient.setBodyExtractor()` with a custom configured `BodyExtractor<Mono<OAuth2AccessTokenResponse>, ReactiveHttpInputMessage>` that is used for converting the OAuth 2.0 Access Token Response to an `OAuth2AccessTokenResponse`.
The default implementation provided by `OAuth2BodyExtractors.oauth2AccessTokenResponse()` parses the response and handles errors accordingly.

=== Customizing the `WebClient`

Alternatively, if your requirements are more advanced, you can take full control of the request/response by simply providing `WebClientReactiveClientCredentialsTokenResponseClient.setWebClient()` with a custom configured `WebClient`.

Whether you customize `WebClientReactiveClientCredentialsTokenResponseClient` or provide your own implementation of `ReactiveOAuth2AccessTokenResponseClient`, you'll need to configure it as shown in the following example:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
// Customize
ReactiveOAuth2AccessTokenResponseClient<OAuth2ClientCredentialsGrantRequest> clientCredentialsTokenResponseClient = ...

ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
		ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
				.clientCredentials(configurer -> configurer.accessTokenResponseClient(clientCredentialsTokenResponseClient))
				.build();

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
// Customize
val clientCredentialsTokenResponseClient: ReactiveOAuth2AccessTokenResponseClient<OAuth2ClientCredentialsGrantRequest> = ...

val authorizedClientProvider: ReactiveOAuth2AuthorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
        .clientCredentials { it.accessTokenResponseClient(clientCredentialsTokenResponseClient) }
        .build()

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
----
======

[NOTE]
`ReactiveOAuth2AuthorizedClientProviderBuilder.builder().clientCredentials()` configures a `ClientCredentialsReactiveOAuth2AuthorizedClientProvider`,
which is an implementation of a `ReactiveOAuth2AuthorizedClientProvider` for the Client Credentials grant.

=== Using the Access Token

Given the following Spring Boot properties for an OAuth 2.0 Client registration:

[source,yaml]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-secret: okta-client-secret
            authorization-grant-type: client_credentials
            scope: read, write
        provider:
          okta:
            token-uri: https://dev-1234.oktapreview.com/oauth2/v1/token
----

...and the `ReactiveOAuth2AuthorizedClientManager` `@Bean`:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
public ReactiveOAuth2AuthorizedClientManager authorizedClientManager(
		ReactiveClientRegistrationRepository clientRegistrationRepository,
		ServerOAuth2AuthorizedClientRepository authorizedClientRepository) {

	ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
			ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
					.clientCredentials()
					.build();

	DefaultReactiveOAuth2AuthorizedClientManager authorizedClientManager =
			new DefaultReactiveOAuth2AuthorizedClientManager(
					clientRegistrationRepository, authorizedClientRepository);
	authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);

	return authorizedClientManager;
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
fun authorizedClientManager(
        clientRegistrationRepository: ReactiveClientRegistrationRepository,
        authorizedClientRepository: ServerOAuth2AuthorizedClientRepository): ReactiveOAuth2AuthorizedClientManager {
    val authorizedClientProvider: ReactiveOAuth2AuthorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
            .clientCredentials()
            .build()
    val authorizedClientManager = DefaultReactiveOAuth2AuthorizedClientManager(
            clientRegistrationRepository, authorizedClientRepository)
    authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
    return authorizedClientManager
}
----
======

You may obtain the `OAuth2AccessToken` as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Controller
public class OAuth2ClientController {

	@Autowired
	private ReactiveOAuth2AuthorizedClientManager authorizedClientManager;

	@GetMapping("/")
	public Mono<String> index(Authentication authentication, ServerWebExchange exchange) {
		OAuth2AuthorizeRequest authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
				.principal(authentication)
				.attribute(ServerWebExchange.class.getName(), exchange)
				.build();

		return this.authorizedClientManager.authorize(authorizeRequest)
				.map(OAuth2AuthorizedClient::getAccessToken)
				...
				.thenReturn("index");
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
class OAuth2ClientController {

    @Autowired
    private lateinit var authorizedClientManager: ReactiveOAuth2AuthorizedClientManager

    @GetMapping("/")
    fun index(authentication: Authentication, exchange: ServerWebExchange): Mono<String> {
        val authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
                .principal(authentication)
                .attribute(ServerWebExchange::class.java.name, exchange)
                .build()

        return authorizedClientManager.authorize(authorizeRequest)
                .map { it.accessToken }
                ...
                .thenReturn("index")
    }
}
----
======

[NOTE]
`ServerWebExchange` is an OPTIONAL attribute.
If not provided, it will be obtained from the https://projectreactor.io/docs/core/release/reference/#context[Reactor's Context] via the key `ServerWebExchange.class`.


[[oauth2Client-password-grant]]
== Resource Owner Password Credentials

[NOTE]
Please refer to the OAuth 2.0 Authorization Framework for further details on the https://tools.ietf.org/html/rfc6749#section-1.3.3[Resource Owner Password Credentials] grant.


=== Requesting an Access Token

[NOTE]
Please refer to the https://tools.ietf.org/html/rfc6749#section-4.3.2[Access Token Request/Response] protocol flow for the Resource Owner Password Credentials grant.

The default implementation of `ReactiveOAuth2AccessTokenResponseClient` for the Resource Owner Password Credentials grant is `WebClientReactivePasswordTokenResponseClient`, which uses a `WebClient` when requesting an access token at the Authorization Server’s Token Endpoint.

The `WebClientReactivePasswordTokenResponseClient` is quite flexible as it allows you to customize the pre-processing of the Token Request and/or post-handling of the Token Response.


=== Customizing the Access Token Request

If you need to customize the pre-processing of the Token Request, you can provide `WebClientReactivePasswordTokenResponseClient.setParametersConverter()` with a custom `Converter<OAuth2PasswordGrantRequest, MultiValueMap<String, String>>`.
The default implementation builds a `MultiValueMap<String, String>` containing only the `grant_type` parameter of a standard https://tools.ietf.org/html/rfc6749#section-4.4.2[OAuth 2.0 Access Token Request] which is used to construct the request. Other parameters required by the Resource Owner Password Credentials grant are added directly to the body of the request by the `WebClientReactivePasswordTokenResponseClient`.
However, providing a custom `Converter`, would allow you to extend the standard Token Request and add custom parameter(s).

[TIP]
If you prefer to only add additional parameters, you can instead provide `WebClientReactivePasswordTokenResponseClient.addParametersConverter()` with a custom `Converter<OAuth2PasswordGrantRequest, MultiValueMap<String, String>>` which constructs an aggregate `Converter`.

IMPORTANT: The custom `Converter` must return valid parameters of an OAuth 2.0 Access Token Request that is understood by the intended OAuth 2.0 Provider.


=== Customizing the Access Token Response

On the other end, if you need to customize the post-handling of the Token Response, you will need to provide `WebClientReactivePasswordTokenResponseClient.setBodyExtractor()` with a custom configured `BodyExtractor<Mono<OAuth2AccessTokenResponse>, ReactiveHttpInputMessage>` that is used for converting the OAuth 2.0 Access Token Response to an `OAuth2AccessTokenResponse`.
The default implementation provided by `OAuth2BodyExtractors.oauth2AccessTokenResponse()` parses the response and handles errors accordingly.

=== Customizing the `WebClient`

Alternatively, if your requirements are more advanced, you can take full control of the request/response by simply providing `WebClientReactivePasswordTokenResponseClient.setWebClient()` with a custom configured `WebClient`.

Whether you customize `WebClientReactivePasswordTokenResponseClient` or provide your own implementation of `ReactiveOAuth2AccessTokenResponseClient`, you'll need to configure it as shown in the following example:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
// Customize
ReactiveOAuth2AccessTokenResponseClient<OAuth2PasswordGrantRequest> passwordTokenResponseClient = ...

ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
		ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
				.password(configurer -> configurer.accessTokenResponseClient(passwordTokenResponseClient))
				.refreshToken()
				.build();

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
val passwordTokenResponseClient: ReactiveOAuth2AccessTokenResponseClient<OAuth2PasswordGrantRequest> = ...

val authorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
        .password { it.accessTokenResponseClient(passwordTokenResponseClient) }
        .refreshToken()
        .build()

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
----
======

[NOTE]
`ReactiveOAuth2AuthorizedClientProviderBuilder.builder().password()` configures a `PasswordReactiveOAuth2AuthorizedClientProvider`,
which is an implementation of a `ReactiveOAuth2AuthorizedClientProvider` for the Resource Owner Password Credentials grant.

=== Using the Access Token

Given the following Spring Boot properties for an OAuth 2.0 Client registration:

[source,yaml]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-secret: okta-client-secret
            authorization-grant-type: password
            scope: read, write
        provider:
          okta:
            token-uri: https://dev-1234.oktapreview.com/oauth2/v1/token
----

...and the `ReactiveOAuth2AuthorizedClientManager` `@Bean`:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
public ReactiveOAuth2AuthorizedClientManager authorizedClientManager(
		ReactiveClientRegistrationRepository clientRegistrationRepository,
		ServerOAuth2AuthorizedClientRepository authorizedClientRepository) {

	ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
			ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
					.password()
					.refreshToken()
					.build();

	DefaultReactiveOAuth2AuthorizedClientManager authorizedClientManager =
			new DefaultReactiveOAuth2AuthorizedClientManager(
					clientRegistrationRepository, authorizedClientRepository);
	authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);

	// Assuming the `username` and `password` are supplied as `ServerHttpRequest` parameters,
	// map the `ServerHttpRequest` parameters to `OAuth2AuthorizationContext.getAttributes()`
	authorizedClientManager.setContextAttributesMapper(contextAttributesMapper());

	return authorizedClientManager;
}

private Function<OAuth2AuthorizeRequest, Mono<Map<String, Object>>> contextAttributesMapper() {
	return authorizeRequest -> {
		Map<String, Object> contextAttributes = Collections.emptyMap();
		ServerWebExchange exchange = authorizeRequest.getAttribute(ServerWebExchange.class.getName());
		ServerHttpRequest request = exchange.getRequest();
		String username = request.getQueryParams().getFirst(OAuth2ParameterNames.USERNAME);
		String password = request.getQueryParams().getFirst(OAuth2ParameterNames.PASSWORD);
		if (StringUtils.hasText(username) && StringUtils.hasText(password)) {
			contextAttributes = new HashMap<>();

			// `PasswordReactiveOAuth2AuthorizedClientProvider` requires both attributes
			contextAttributes.put(OAuth2AuthorizationContext.USERNAME_ATTRIBUTE_NAME, username);
			contextAttributes.put(OAuth2AuthorizationContext.PASSWORD_ATTRIBUTE_NAME, password);
		}
		return Mono.just(contextAttributes);
	};
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
fun authorizedClientManager(
        clientRegistrationRepository: ReactiveClientRegistrationRepository,
        authorizedClientRepository: ServerOAuth2AuthorizedClientRepository): ReactiveOAuth2AuthorizedClientManager {
    val authorizedClientProvider: ReactiveOAuth2AuthorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
            .password()
            .refreshToken()
            .build()
    val authorizedClientManager = DefaultReactiveOAuth2AuthorizedClientManager(
            clientRegistrationRepository, authorizedClientRepository)
    authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)

    // Assuming the `username` and `password` are supplied as `ServerHttpRequest` parameters,
    // map the `ServerHttpRequest` parameters to `OAuth2AuthorizationContext.getAttributes()`
    authorizedClientManager.setContextAttributesMapper(contextAttributesMapper())
    return authorizedClientManager
}

private fun contextAttributesMapper(): Function<OAuth2AuthorizeRequest, Mono<MutableMap<String, Any>>> {
    return Function { authorizeRequest ->
        var contextAttributes: MutableMap<String, Any> = mutableMapOf()
        val exchange: ServerWebExchange = authorizeRequest.getAttribute(ServerWebExchange::class.java.name)!!
        val request: ServerHttpRequest = exchange.request
        val username: String? = request.queryParams.getFirst(OAuth2ParameterNames.USERNAME)
        val password: String? = request.queryParams.getFirst(OAuth2ParameterNames.PASSWORD)
        if (StringUtils.hasText(username) && StringUtils.hasText(password)) {
            contextAttributes = hashMapOf()

            // `PasswordReactiveOAuth2AuthorizedClientProvider` requires both attributes
            contextAttributes[OAuth2AuthorizationContext.USERNAME_ATTRIBUTE_NAME] = username!!
            contextAttributes[OAuth2AuthorizationContext.PASSWORD_ATTRIBUTE_NAME] = password!!
        }
        Mono.just(contextAttributes)
    }
}
----
======

You may obtain the `OAuth2AccessToken` as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Controller
public class OAuth2ClientController {

	@Autowired
	private ReactiveOAuth2AuthorizedClientManager authorizedClientManager;

	@GetMapping("/")
	public Mono<String> index(Authentication authentication, ServerWebExchange exchange) {
		OAuth2AuthorizeRequest authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
				.principal(authentication)
				.attribute(ServerWebExchange.class.getName(), exchange)
				.build();

		return this.authorizedClientManager.authorize(authorizeRequest)
				.map(OAuth2AuthorizedClient::getAccessToken)
				...
				.thenReturn("index");
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Controller
class OAuth2ClientController {
    @Autowired
    private lateinit var authorizedClientManager: ReactiveOAuth2AuthorizedClientManager

    @GetMapping("/")
    fun index(authentication: Authentication, exchange: ServerWebExchange): Mono<String> {
        val authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
                .principal(authentication)
                .attribute(ServerWebExchange::class.java.name, exchange)
                .build()

        return authorizedClientManager.authorize(authorizeRequest)
                .map { it.accessToken }
                ...
                .thenReturn("index")
    }
}
----
======

[NOTE]
`ServerWebExchange` is an OPTIONAL attribute.
If not provided, it will be obtained from the https://projectreactor.io/docs/core/release/reference/#context[Reactor's Context] via the key `ServerWebExchange.class`.


[[oauth2Client-jwt-bearer-grant]]
== JWT Bearer

[NOTE]
Please refer to JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants for further details on the https://datatracker.ietf.org/doc/html/rfc7523[JWT Bearer] grant.


=== Requesting an Access Token

[NOTE]
Please refer to the https://datatracker.ietf.org/doc/html/rfc7523#section-2.1[Access Token Request/Response] protocol flow for the JWT Bearer grant.

The default implementation of `ReactiveOAuth2AccessTokenResponseClient` for the JWT Bearer grant is `WebClientReactiveJwtBearerTokenResponseClient`, which uses a `WebClient` when requesting an access token at the Authorization Server’s Token Endpoint.

The `WebClientReactiveJwtBearerTokenResponseClient` is quite flexible as it allows you to customize the pre-processing of the Token Request and/or post-handling of the Token Response.


=== Customizing the Access Token Request

If you need to customize the pre-processing of the Token Request, you can provide `WebClientReactiveJwtBearerTokenResponseClient.setParametersConverter()` with a custom `Converter<JwtBearerGrantRequest, MultiValueMap<String, String>>`.
The default implementation builds a `MultiValueMap<String, String>` containing only the `grant_type` parameter of a standard https://tools.ietf.org/html/rfc6749#section-4.4.2[OAuth 2.0 Access Token Request] which is used to construct the request. Other parameters required by the JWT Bearer grant are added directly to the body of the request by the `WebClientReactiveJwtBearerTokenResponseClient`.
However, providing a custom `Converter`, would allow you to extend the standard Token Request and add custom parameter(s).

[TIP]
If you prefer to only add additional parameters, you can instead provide `WebClientReactiveJwtBearerTokenResponseClient.addParametersConverter()` with a custom `Converter<JwtBearerGrantRequest, MultiValueMap<String, String>>` which constructs an aggregate `Converter`.

IMPORTANT: The custom `Converter` must return valid parameters of an OAuth 2.0 Access Token Request that is understood by the intended OAuth 2.0 Provider.

=== Customizing the Access Token Response

On the other end, if you need to customize the post-handling of the Token Response, you will need to provide `WebClientReactiveJwtBearerTokenResponseClient.setBodyExtractor()` with a custom configured `BodyExtractor<Mono<OAuth2AccessTokenResponse>, ReactiveHttpInputMessage>` that is used for converting the OAuth 2.0 Access Token Response to an `OAuth2AccessTokenResponse`.
The default implementation provided by `OAuth2BodyExtractors.oauth2AccessTokenResponse()` parses the response and handles errors accordingly.

=== Customizing the `WebClient`

Alternatively, if your requirements are more advanced, you can take full control of the request/response by simply providing `WebClientReactiveJwtBearerTokenResponseClient.setWebClient()` with a custom configured `WebClient`.

Whether you customize `WebClientReactiveJwtBearerTokenResponseClient` or provide your own implementation of `ReactiveOAuth2AccessTokenResponseClient`, you'll need to configure it as shown in the following example:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
// Customize
ReactiveOAuth2AccessTokenResponseClient<JwtBearerGrantRequest> jwtBearerTokenResponseClient = ...

JwtBearerReactiveOAuth2AuthorizedClientProvider jwtBearerAuthorizedClientProvider = new JwtBearerReactiveOAuth2AuthorizedClientProvider();
jwtBearerAuthorizedClientProvider.setAccessTokenResponseClient(jwtBearerTokenResponseClient);

ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
		ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
				.provider(jwtBearerAuthorizedClientProvider)
				.build();

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
// Customize
val jwtBearerTokenResponseClient: ReactiveOAuth2AccessTokenResponseClient<JwtBearerGrantRequest> = ...

val jwtBearerAuthorizedClientProvider = JwtBearerReactiveOAuth2AuthorizedClientProvider()
jwtBearerAuthorizedClientProvider.setAccessTokenResponseClient(jwtBearerTokenResponseClient)

val authorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
        .provider(jwtBearerAuthorizedClientProvider)
        .build()

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
----
======

=== Using the Access Token

Given the following Spring Boot properties for an OAuth 2.0 Client registration:

[source,yaml]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-secret: okta-client-secret
            authorization-grant-type: urn:ietf:params:oauth:grant-type:jwt-bearer
            scope: read
        provider:
          okta:
            token-uri: https://dev-1234.oktapreview.com/oauth2/v1/token
----

...and the `OAuth2AuthorizedClientManager` `@Bean`:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
public ReactiveOAuth2AuthorizedClientManager authorizedClientManager(
		ReactiveClientRegistrationRepository clientRegistrationRepository,
		ServerOAuth2AuthorizedClientRepository authorizedClientRepository) {

	JwtBearerReactiveOAuth2AuthorizedClientProvider jwtBearerAuthorizedClientProvider =
			new JwtBearerReactiveOAuth2AuthorizedClientProvider();

	ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
			ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
					.provider(jwtBearerAuthorizedClientProvider)
					.build();

	DefaultReactiveOAuth2AuthorizedClientManager authorizedClientManager =
			new DefaultReactiveOAuth2AuthorizedClientManager(
					clientRegistrationRepository, authorizedClientRepository);
	authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);

	return authorizedClientManager;
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
fun authorizedClientManager(
        clientRegistrationRepository: ReactiveClientRegistrationRepository,
        authorizedClientRepository: ServerOAuth2AuthorizedClientRepository): ReactiveOAuth2AuthorizedClientManager {
    val jwtBearerAuthorizedClientProvider = JwtBearerReactiveOAuth2AuthorizedClientProvider()
    val authorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
            .provider(jwtBearerAuthorizedClientProvider)
            .build()
    val authorizedClientManager = DefaultReactiveOAuth2AuthorizedClientManager(
            clientRegistrationRepository, authorizedClientRepository)
    authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
    return authorizedClientManager
}
----
======

You may obtain the `OAuth2AccessToken` as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@RestController
public class OAuth2ResourceServerController {

	@Autowired
	private ReactiveOAuth2AuthorizedClientManager authorizedClientManager;

	@GetMapping("/resource")
	public Mono<String> resource(JwtAuthenticationToken jwtAuthentication, ServerWebExchange exchange) {
		OAuth2AuthorizeRequest authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
				.principal(jwtAuthentication)
				.build();

		return this.authorizedClientManager.authorize(authorizeRequest)
				.map(OAuth2AuthorizedClient::getAccessToken)
				...
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
class OAuth2ResourceServerController {

    @Autowired
    private lateinit var authorizedClientManager: ReactiveOAuth2AuthorizedClientManager

    @GetMapping("/resource")
    fun resource(jwtAuthentication: JwtAuthenticationToken, exchange: ServerWebExchange): Mono<String> {
        val authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
                .principal(jwtAuthentication)
                .build()
        return authorizedClientManager.authorize(authorizeRequest)
                .map { it.accessToken }
                ...
    }
}
----
======

[NOTE]
`JwtBearerReactiveOAuth2AuthorizedClientProvider` resolves the `Jwt` assertion via `OAuth2AuthorizationContext.getPrincipal().getPrincipal()` by default, hence the use of `JwtAuthenticationToken` in the preceding example.

[TIP]
If you need to resolve the `Jwt` assertion from a different source, you can provide `JwtBearerReactiveOAuth2AuthorizedClientProvider.setJwtAssertionResolver()` with a custom `Function<OAuth2AuthorizationContext, Mono<Jwt>>`.

[[oauth2Client-token-exchange-grant]]
== Token Exchange

[NOTE]
Please refer to OAuth 2.0 Token Exchange for further details on the https://datatracker.ietf.org/doc/html/rfc8693[Token Exchange] grant.


=== Requesting an Access Token

[NOTE]
Please refer to the https://datatracker.ietf.org/doc/html/rfc8693#section-2[Token Exchange Request and Response] protocol flow for the Token Exchange grant.

The default implementation of `ReactiveOAuth2AccessTokenResponseClient` for the Token Exchange grant is `WebClientReactiveTokenExchangeTokenResponseClient`, which uses a `WebClient` when requesting an access token at the Authorization Server’s Token Endpoint.

The `WebClientReactiveTokenExchangeTokenResponseClient` is quite flexible as it allows you to customize the pre-processing of the Token Request and/or post-handling of the Token Response.


=== Customizing the Access Token Request

If you need to customize the pre-processing of the Token Request, you can provide `WebClientReactiveTokenExchangeTokenResponseClient.setParametersConverter()` with a custom `Converter<TokenExchangeGrantRequest, MultiValueMap<String, String>>`.
The default implementation builds a `MultiValueMap<String, String>` containing only the `grant_type` parameter of a standard https://tools.ietf.org/html/rfc6749#section-4.4.2[OAuth 2.0 Access Token Request] which is used to construct the request.
Other parameters required by the Token Exchange grant are added directly to the body of the request by the `WebClientReactiveTokenExchangeTokenResponseClient`.
However, providing a custom `Converter`, would allow you to extend the standard Token Request and add custom parameter(s).

[TIP]
If you prefer to only add additional parameters, you can instead provide `WebClientReactiveTokenExchangeTokenResponseClient.addParametersConverter()` with a custom `Converter<TokenExchangeGrantRequest, MultiValueMap<String, String>>` which constructs an aggregate `Converter`.

IMPORTANT: The custom `Converter` must return valid parameters of an OAuth 2.0 Access Token Request that is understood by the intended OAuth 2.0 Provider.

=== Customizing the Access Token Response

On the other end, if you need to customize the post-handling of the Token Response, you will need to provide `WebClientReactiveTokenExchangeTokenResponseClient.setBodyExtractor()` with a custom configured `BodyExtractor<Mono<OAuth2AccessTokenResponse>, ReactiveHttpInputMessage>` that is used for converting the OAuth 2.0 Access Token Response to an `OAuth2AccessTokenResponse`.
The default implementation provided by `OAuth2BodyExtractors.oauth2AccessTokenResponse()` parses the response and handles errors accordingly.

=== Customizing the `WebClient`

Alternatively, if your requirements are more advanced, you can take full control of the request/response by simply providing `WebClientReactiveTokenExchangeTokenResponseClient.setWebClient()` with a custom configured `WebClient`.

Whether you customize `WebClientReactiveTokenExchangeTokenResponseClient` or provide your own implementation of `ReactiveOAuth2AccessTokenResponseClient`, you'll need to configure it as shown in the following example:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
// Customize
ReactiveOAuth2AccessTokenResponseClient<TokenExchangeGrantRequest> tokenExchangeTokenResponseClient = ...

TokenExchangeReactiveOAuth2AuthorizedClientProvider tokenExchangeAuthorizedClientProvider = new TokenExchangeReactiveOAuth2AuthorizedClientProvider();
tokenExchangeAuthorizedClientProvider.setAccessTokenResponseClient(tokenExchangeTokenResponseClient);

ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
		ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
				.provider(tokenExchangeAuthorizedClientProvider)
				.build();

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
// Customize
val tokenExchangeTokenResponseClient: ReactiveOAuth2AccessTokenResponseClient<TokenExchangeGrantRequest> = ...

val tokenExchangeAuthorizedClientProvider = TokenExchangeReactiveOAuth2AuthorizedClientProvider()
tokenExchangeAuthorizedClientProvider.setAccessTokenResponseClient(tokenExchangeTokenResponseClient)

val authorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
        .provider(tokenExchangeAuthorizedClientProvider)
        .build()

...

authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
----
======

=== Using the Access Token

Given the following Spring Boot properties for an OAuth 2.0 Client registration:

[source,yaml]
----
spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-secret: okta-client-secret
            authorization-grant-type: urn:ietf:params:oauth:grant-type:token-exchange
            scope: read
        provider:
          okta:
            token-uri: https://dev-1234.oktapreview.com/oauth2/v1/token
----

...and the `OAuth2AuthorizedClientManager` `@Bean`:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
public ReactiveOAuth2AuthorizedClientManager authorizedClientManager(
		ReactiveClientRegistrationRepository clientRegistrationRepository,
		ServerOAuth2AuthorizedClientRepository authorizedClientRepository) {

	TokenExchangeReactiveOAuth2AuthorizedClientProvider tokenExchangeAuthorizedClientProvider =
			new TokenExchangeReactiveOAuth2AuthorizedClientProvider();

	ReactiveOAuth2AuthorizedClientProvider authorizedClientProvider =
			ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
					.provider(tokenExchangeAuthorizedClientProvider)
					.build();

	DefaultReactiveOAuth2AuthorizedClientManager authorizedClientManager =
			new DefaultReactiveOAuth2AuthorizedClientManager(
					clientRegistrationRepository, authorizedClientRepository);
	authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider);

	return authorizedClientManager;
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
fun authorizedClientManager(
        clientRegistrationRepository: ReactiveClientRegistrationRepository,
        authorizedClientRepository: ServerOAuth2AuthorizedClientRepository): ReactiveOAuth2AuthorizedClientManager {
    val tokenExchangeAuthorizedClientProvider = TokenExchangeReactiveOAuth2AuthorizedClientProvider()
    val authorizedClientProvider = ReactiveOAuth2AuthorizedClientProviderBuilder.builder()
            .provider(tokenExchangeAuthorizedClientProvider)
            .build()
    val authorizedClientManager = DefaultReactiveOAuth2AuthorizedClientManager(
            clientRegistrationRepository, authorizedClientRepository)
    authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
    return authorizedClientManager
}
----
======

You may obtain the `OAuth2AccessToken` as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@RestController
public class OAuth2ResourceServerController {

	@Autowired
	private ReactiveOAuth2AuthorizedClientManager authorizedClientManager;

	@GetMapping("/resource")
	public Mono<String> resource(JwtAuthenticationToken jwtAuthentication) {
		OAuth2AuthorizeRequest authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
				.principal(jwtAuthentication)
				.build();

		return this.authorizedClientManager.authorize(authorizeRequest)
				.map(OAuth2AuthorizedClient::getAccessToken)
				...
	}
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
class OAuth2ResourceServerController {

    @Autowired
    private lateinit var authorizedClientManager: ReactiveOAuth2AuthorizedClientManager

    @GetMapping("/resource")
    fun resource(jwtAuthentication: JwtAuthenticationToken): Mono<String> {
        val authorizeRequest = OAuth2AuthorizeRequest.withClientRegistrationId("okta")
                .principal(jwtAuthentication)
                .build()
        return authorizedClientManager.authorize(authorizeRequest)
                .map { it.accessToken }
                ...
    }
}
----
======

[NOTE]
`TokenExchangeReactiveOAuth2AuthorizedClientProvider` resolves the subject token (as an `OAuth2Token`) via `OAuth2AuthorizationContext.getPrincipal().getPrincipal()` by default, hence the use of `JwtAuthenticationToken` in the preceding example.
An actor token is not resolved by default.

[TIP]
If you need to resolve the subject token from a different source, you can provide `TokenExchangeReactiveOAuth2AuthorizedClientProvider.setSubjectTokenResolver()` with a custom `Function<OAuth2AuthorizationContext, Mono<OAuth2Token>>`.

[TIP]
If you need to resolve an actor token, you can provide `TokenExchangeReactiveOAuth2AuthorizedClientProvider.setActorTokenResolver()` with a custom `Function<OAuth2AuthorizationContext, Mono<OAuth2Token>>`.