Unsupported code_challenge_method parameter should return invalid_grant

Issue gh-770

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/authentication/CodeVerifierAuthenticator.java

@@ -122,9 +122,10 @@ final class CodeVerifierAuthenticator {
 			} catch (NoSuchAlgorithmException ex) {
 				// It is unlikely that SHA-256 is not available on the server. If it is not available,
 				// there will likely be bigger issues as well. We default to SERVER_ERROR.
+				throw new OAuth2AuthenticationException(OAuth2ErrorCodes.SERVER_ERROR);
 			}
 		}
-		throw new OAuth2AuthenticationException(OAuth2ErrorCodes.SERVER_ERROR);
+		return false;
 	}
 
 	private static void throwInvalidGrant(String parameterName) {

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/authentication/PublicClientAuthenticationProviderTests.java

@@ -275,7 +275,7 @@ public class PublicClientAuthenticationProviderTests {
 				.isInstanceOf(OAuth2AuthenticationException.class)
 				.extracting(ex -> ((OAuth2AuthenticationException) ex).getError())
 				.extracting("errorCode")
-				.isEqualTo(OAuth2ErrorCodes.SERVER_ERROR);
+				.isEqualTo(OAuth2ErrorCodes.INVALID_GRANT);
 	}
 
 	private static Map<String, Object> createAuthorizationCodeTokenParameters() {