Trim OAuth2 provider property whitespace

Update `OAuth2ClientPropertiesRegistrationAdapter` to trim whitespace
of the "provider" property.

See gh-17497

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/oauth2/client/OAuth2ClientPropertiesRegistrationAdapter.java

@@ -56,9 +56,10 @@ public final class OAuth2ClientPropertiesRegistrationAdapter {
 
 	private static ClientRegistration getClientRegistration(String registrationId,
 			OAuth2ClientProperties.Registration properties, Map<String, Provider> providers) {
-		Builder builder = getBuilderFromIssuerIfPossible(registrationId, properties.getProvider(), providers);
+		String provider = StringUtils.trimWhitespace(properties.getProvider());
+		Builder builder = getBuilderFromIssuerIfPossible(registrationId, provider, providers);
 		if (builder == null) {
-			builder = getBuilder(registrationId, properties.getProvider(), providers);
+			builder = getBuilder(registrationId, provider, providers);
 		}
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
 		map.from(properties::getClientId).to(builder::clientId);

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/security/oauth2/client/OAuth2ClientPropertiesRegistrationAdapterTests.java

@@ -251,6 +251,31 @@ public class OAuth2ClientPropertiesRegistrationAdapterTests {
 		assertThat(userInfoEndpoint.getUserNameAttributeName()).isEqualTo("sub");
 	}
 
+	@Test
+	public void getClientRegistrationsWhenRegistrationProviderPropertyShouldBeTrimmed() {
+		OAuth2ClientProperties properties = new OAuth2ClientProperties();
+		OAuth2ClientProperties.Registration registration = createRegistration("  provider  ");
+		Provider provider = createProvider();
+		properties.getProvider().put("provider", provider);
+		properties.getRegistration().put("registration", registration);
+		assertThat(OAuth2ClientPropertiesRegistrationAdapter.getClientRegistrations(properties)).isNotEmpty();
+	}
+
+	@Test
+	public void getClientRegistrationsWhenRegistrationProviderPropertyWithIssuerShouldBeTrimmed() throws Exception {
+		this.server = new MockWebServer();
+		this.server.start();
+		String issuer = this.server.url("").toString();
+		setupMockResponse(issuer);
+		OAuth2ClientProperties properties = new OAuth2ClientProperties();
+		OAuth2ClientProperties.Registration registration = createRegistration("   provider  ");
+		Provider provider = createProvider();
+		provider.setIssuerUri(issuer);
+		properties.getProvider().put("provider", provider);
+		properties.getRegistration().put("registration", registration);
+		assertThat(OAuth2ClientPropertiesRegistrationAdapter.getClientRegistrations(properties)).isNotEmpty();
+	}
+
 	private Provider createProvider() {
 		Provider provider = new Provider();
 		provider.setAuthorizationUri("https://example.com/auth");