
[[how-to-multitenancy]]
= How-to: Implement Multitenancy
:index-link: ../how-to.html
:docs-dir: ..

This guide shows how to customize Spring Authorization Server to support multiple issuers per host in a multi-tenant hosting configuration.
The purpose of this guide is to demonstrate a general pattern for building multi-tenant capable components for Spring Authorization Server, which can also be applied to other components to suit your needs.

* xref:guides/how-to-multitenancy.adoc#multi-tenant-enable-multiple-issuers[Enable multiple issuers]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-define-tenant-identifier[Define the tenant identifier]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-create-component-registry[Create a component registry]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-create-components[Create multi-tenant components]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-add-tenants-dynamically[Add tenants dynamically]

[[multi-tenant-enable-multiple-issuers]]
== Enable multiple issuers

Support for using multiple issuers per host is disabled by default.
To enable, add the following configuration:

.AuthorizationServerSettingsConfig
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/AuthorizationServerSettingsConfig.java[]
----

<1> Set to `true` to allow usage of multiple issuers per host.

WARNING: Do not allow for any arbitrary issuer to be used. An allowlist of approved issuers should be enforced.

[[multi-tenant-define-tenant-identifier]]
== Define the tenant identifier

The xref:protocol-endpoints.adoc#oidc-provider-configuration-endpoint[OpenID Connect 1.0 Provider Configuration Endpoint] and xref:protocol-endpoints.adoc#oauth2-authorization-server-metadata-endpoint[OAuth2 Authorization Server Metadata Endpoint] allow for path components in the issuer identifier value, which effectively enables supporting multiple issuers per host.

For example, an https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderConfigurationRequest[OpenID Provider Configuration Request] "http://localhost:9000/issuer1/.well-known/openid-configuration" or an https://datatracker.ietf.org/doc/html/rfc8414#section-3.1[Authorization Server Metadata Request] "http://localhost:9000/.well-known/oauth-authorization-server/issuer1" would return the following configuration metadata:

[source,json]
----
{
  "issuer": "http://localhost:9000/issuer1",
  "authorization_endpoint": "http://localhost:9000/issuer1/oauth2/authorize",
  "token_endpoint": "http://localhost:9000/issuer1/oauth2/token",
  "jwks_uri": "http://localhost:9000/issuer1/oauth2/jwks",
  "revocation_endpoint": "http://localhost:9000/issuer1/oauth2/revoke",
  "introspection_endpoint": "http://localhost:9000/issuer1/oauth2/introspect",
  ...
}
----

NOTE: The base URL of the xref:protocol-endpoints.adoc[Protocol Endpoints] is the issuer identifier value.

Essentially, an issuer identifier with a path component represents the _"tenant identifier"_.

[[multi-tenant-create-component-registry]]
== Create a component registry

We start by building a simple registry for managing the concrete components for each tenant.
The registry contains the logic for retrieving a concrete implementation of a particular class using the issuer identifier value.

We will use the following class in each of the delegating implementations below:

.TenantPerIssuerComponentRegistry
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/TenantPerIssuerComponentRegistry.java[]
----

TIP: This registry is designed to allow components to be easily registered at startup to support adding tenants statically, but also supports xref:guides/how-to-multitenancy.adoc#multi-tenant-add-tenants-dynamically[adding tenants dynamically] at runtime.

[[multi-tenant-create-components]]
== Create multi-tenant components

The components that require multi-tenant capability are:

* xref:guides/how-to-multitenancy.adoc#multi-tenant-registered-client-repository[`RegisteredClientRepository`]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-oauth2-authorization-service[`OAuth2AuthorizationService`]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-oauth2-authorization-consent-service[`OAuth2AuthorizationConsentService`]
* xref:guides/how-to-multitenancy.adoc#multi-tenant-jwk-source[`JWKSource<SecurityContext>`]

For each of these components, an implementation of a composite can be provided that delegates to the concrete component associated to the _"requested"_ issuer identifier.

Let's step through a scenario of how to customize Spring Authorization Server to support 2x tenants for each multi-tenant capable component.

[[multi-tenant-registered-client-repository]]
=== Multi-tenant RegisteredClientRepository

The following example shows a sample implementation of a xref:core-model-components.adoc#registered-client-repository[`RegisteredClientRepository`] that is composed of 2x `JdbcRegisteredClientRepository` instances, where each instance is mapped to an issuer identifier:

.RegisteredClientRepositoryConfig
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/RegisteredClientRepositoryConfig.java[]
----

TIP: Click on the "Expand folded text" icon in the code sample above to display the full example.

<1> A `JdbcRegisteredClientRepository` instance mapped to issuer identifier `issuer1` and using a dedicated `DataSource`.
<2> A `JdbcRegisteredClientRepository` instance mapped to issuer identifier `issuer2` and using a dedicated `DataSource`.
<3> A composite implementation of a `RegisteredClientRepository` that delegates to a `JdbcRegisteredClientRepository` mapped to the _"requested"_ issuer identifier.
<4> Obtain the `JdbcRegisteredClientRepository` that is mapped to the _"requested"_ issuer identifier indicated by `AuthorizationServerContext.getIssuer()`.

IMPORTANT: Explicitly configuring the issuer identifier via `AuthorizationServerSettings.builder().issuer("http://localhost:9000")` forces to a single-tenant configuration. Avoid explicitly configuring the issuer identifier when using a multi-tenant hosting configuration.

In the preceding example, each of the `JdbcRegisteredClientRepository` instances are configured with a `JdbcTemplate` and associated `DataSource`.
This is important in a multi-tenant configuration as a primary requirement is to have the ability to isolate the data from each tenant.

Configuring a dedicated `DataSource` for each component instance provides the flexibility to isolate the data in its own schema within the same database instance or alternatively isolate the data in a separate database instance altogether.

The following example shows a sample configuration of 2x `DataSource` `@Bean` (one for each tenant) that are used by the multi-tenant capable components:

.DataSourceConfig
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/DataSourceConfig.java[]
----

<1> Use a separate H2 database instance using `issuer1-db` as the name.
<2> Use a separate H2 database instance using `issuer2-db` as the name.

[[multi-tenant-oauth2-authorization-service]]
=== Multi-tenant OAuth2AuthorizationService

The following example shows a sample implementation of an xref:core-model-components.adoc#oauth2-authorization-service[`OAuth2AuthorizationService`] that is composed of 2x `JdbcOAuth2AuthorizationService` instances, where each instance is mapped to an issuer identifier:

.OAuth2AuthorizationServiceConfig
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/OAuth2AuthorizationServiceConfig.java[]
----

<1> A `JdbcOAuth2AuthorizationService` instance mapped to issuer identifier `issuer1` and using a dedicated `DataSource`.
<2> A `JdbcOAuth2AuthorizationService` instance mapped to issuer identifier `issuer2` and using a dedicated `DataSource`.
<3> A composite implementation of an `OAuth2AuthorizationService` that delegates to a `JdbcOAuth2AuthorizationService` mapped to the _"requested"_ issuer identifier.
<4> Obtain the `JdbcOAuth2AuthorizationService` that is mapped to the _"requested"_ issuer identifier indicated by `AuthorizationServerContext.getIssuer()`.

[[multi-tenant-oauth2-authorization-consent-service]]
=== Multi-tenant OAuth2AuthorizationConsentService

The following example shows a sample implementation of an xref:core-model-components.adoc#oauth2-authorization-consent-service[`OAuth2AuthorizationConsentService`] that is composed of 2x `JdbcOAuth2AuthorizationConsentService` instances, where each instance is mapped to an issuer identifier:

.OAuth2AuthorizationConsentServiceConfig
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/OAuth2AuthorizationConsentServiceConfig.java[]
----

<1> A `JdbcOAuth2AuthorizationConsentService` instance mapped to issuer identifier `issuer1` and using a dedicated `DataSource`.
<2> A `JdbcOAuth2AuthorizationConsentService` instance mapped to issuer identifier `issuer2` and using a dedicated `DataSource`.
<3> A composite implementation of an `OAuth2AuthorizationConsentService` that delegates to a `JdbcOAuth2AuthorizationConsentService` mapped to the _"requested"_ issuer identifier.
<4> Obtain the `JdbcOAuth2AuthorizationConsentService` that is mapped to the _"requested"_ issuer identifier indicated by `AuthorizationServerContext.getIssuer()`.

[[multi-tenant-jwk-source]]
=== Multi-tenant JWKSource

And finally, the following example shows a sample implementation of a `JWKSource<SecurityContext>` that is composed of 2x `JWKSet` instances, where each instance is mapped to an issuer identifier:

.JWKSourceConfig
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/JWKSourceConfig.java[]
----

<1> A `JWKSet` instance mapped to issuer identifier `issuer1`.
<2> A `JWKSet` instance mapped to issuer identifier `issuer2`.
<3> A composite implementation of an `JWKSource<SecurityContext>` that uses the `JWKSet` mapped to the _"requested"_ issuer identifier.
<4> Obtain the `JWKSet` that is mapped to the _"requested"_ issuer identifier indicated by `AuthorizationServerContext.getIssuer()`.

[[multi-tenant-add-tenants-dynamically]]
== Add Tenants Dynamically

If the number of tenants is dynamic and can change at runtime, defining each `DataSource` as a `@Bean` may not be feasible.
In this case, the `DataSource` and corresponding components can be registered through other means at application startup and/or runtime.

The following example shows a Spring `@Service` capable of adding tenants dynamically:

.TenantService
[source,java]
----
include::{examples-dir}/main/java/sample/multitenancy/TenantService.java[]
----
