Add ClientRegistration.Builder.registrationId

Fixes: gh-5527

Author: rwinch

oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/registration/ClientRegistration.java

@@ -255,6 +255,17 @@ private Builder(String registrationId) {
 			this.registrationId = registrationId;
 		}
 
+		/**
+		 * Sets the client identifier.
+		 *
+		 * @param registrationId the registration id
+		 * @return the {@link Builder}
+		 */
+		public Builder registrationId(String registrationId) {
+			this.registrationId = registrationId;
+			return this;
+		}
+
 		/**
 		 * Sets the client identifier.
 		 *

oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/registration/ClientRegistrationTests.java

@@ -351,4 +351,24 @@ public void buildWhenImplicitGrantClientNameIsNullThenThrowIllegalArgumentExcept
 			.clientName(null)
 			.build();
 	}
+
+	@Test
+	public void buildWhenOverrideRegistrationIdThenOverridden() {
+		String overriddenId = "override";
+		ClientRegistration registration = ClientRegistration.withRegistrationId(REGISTRATION_ID)
+				.registrationId(overriddenId)
+				.clientId(CLIENT_ID)
+				.clientSecret(CLIENT_SECRET)
+				.clientAuthenticationMethod(ClientAuthenticationMethod.BASIC)
+				.authorizationGrantType(AuthorizationGrantType.AUTHORIZATION_CODE)
+				.redirectUriTemplate(REDIRECT_URI)
+				.scope(SCOPES.toArray(new String[0]))
+				.authorizationUri(AUTHORIZATION_URI)
+				.tokenUri(TOKEN_URI)
+				.jwkSetUri(JWK_SET_URI)
+				.clientName(CLIENT_NAME)
+				.build();
+
+		assertThat(registration.getRegistrationId()).isEqualTo(overriddenId);
+	}
 }