Add support for a singleton Region in AwsIamAuthenticationOptions.

See gh-758

spring-vault-core/src/main/java/org/springframework/vault/authentication/AwsIamAuthenticationOptions.java

@@ -20,6 +20,7 @@ import java.net.URI;
 import software.amazon.awssdk.auth.credentials.AwsCredentials;
 import software.amazon.awssdk.auth.credentials.AwsCredentialsProvider;
 import software.amazon.awssdk.auth.credentials.StaticCredentialsProvider;
+import software.amazon.awssdk.regions.Region;
 import software.amazon.awssdk.regions.providers.AwsRegionProvider;
 import software.amazon.awssdk.regions.providers.DefaultAwsRegionProviderChain;
 
@@ -212,6 +213,19 @@ public class AwsIamAuthenticationOptions {
 			return this;
 		}
 
+		/**
+		 * Configure a {@link Region}, used for computing the signature.
+		 * @param region must not be {@literal null}.
+		 * @return {@code this} {@link AwsIamAuthenticationOptionsBuilder}.
+		 * @since 3.0.2
+		 */
+		public AwsIamAuthenticationOptionsBuilder region(Region region) {
+
+			Assert.notNull(region, "Region must not be null");
+
+			return regionProvider(() -> region);
+		}
+
 		/**
 		 * Configure an {@link AwsRegionProvider}, required to calculate the region to be
 		 * used for computing the signature.

spring-vault-core/src/test/java/org/springframework/vault/authentication/AwsIamAuthenticationUnitTests.java

@@ -89,7 +89,7 @@ class AwsIamAuthenticationUnitTests {
 								+ "}"));
 
 		AwsIamAuthenticationOptions options = AwsIamAuthenticationOptions.builder().role("foo-role")
-				.regionProvider(() -> Region.US_WEST_1).credentials(AwsBasicCredentials.create("foo", "bar")).build();
+				.region(Region.US_WEST_1).credentials(AwsBasicCredentials.create("foo", "bar")).build();
 
 		AuthenticationSteps steps = AwsIamAuthentication.createAuthenticationSteps(options);
 		AuthenticationStepsExecutor executor = new AuthenticationStepsExecutor(steps, this.restTemplate);