Add support for AWS S3 anonymous credentials

Signed-off-by: Paolo Di Tommaso <paolo.ditommaso@gmail.com>

docs/config.rst

@@ -119,6 +119,7 @@ Advanced client configuration options can be set by using the ``client`` attribu
 =========================== ================
 Name                        Description
 =========================== ================
+anonymous                   Allow the access of public S3 buckets without the need to provide AWS credentials. Any service that does not accept unsigned requests will return a service access error.
 s3Acl                       Allow the setting of a predefined bucket permissions also known as *canned ACL*. Permitted values are ``Private``, ``PublicRead``, ``PublicReadWrite``, ``AuthenticatedRead``, ``LogDeliveryWrite``, ``BucketOwnerRead``, ``BucketOwnerFullControl`` and ``AwsExecRead``. See `Amazon docs <https://docs.aws.amazon.com/AmazonS3/latest/userguide/acl-overview.html#canned-acl>`_ for details.
 connectionTimeout           The amount of time to wait (in milliseconds) when initially establishing a connection before giving up and timing out.
 endpoint                    The AWS S3 API entry point e.g. `s3-us-west-1.amazonaws.com`.

plugins/nf-amazon/src/main/com/upplication/s3fs/S3FileSystemProvider.java

@@ -84,6 +84,7 @@
 import com.amazonaws.ClientConfiguration;
 import com.amazonaws.Protocol;
 import com.amazonaws.auth.AWSCredentials;
+import com.amazonaws.auth.AnonymousAWSCredentials;
 import com.amazonaws.auth.BasicAWSCredentials;
 import com.amazonaws.auth.BasicSessionCredentials;
 import com.amazonaws.services.s3.S3ClientOptions;
@@ -863,7 +864,12 @@ protected S3FileSystem createFileSystem0(URI uri, Object accessKey, Object secre
 		AmazonS3Client client;
 		ClientConfiguration config = createClientConfig(props);
 
-		if (accessKey == null && secretKey == null) {
+		final boolean anonymous = "true".equals(props.getProperty("anonymous"));
+		if( anonymous ) {
+			log.debug("Creating AWS S3 client with anonymous credentials");
+			client = new AmazonS3Client(new com.amazonaws.services.s3.AmazonS3Client(new AnonymousAWSCredentials(), config));
+		}
+		else if (accessKey == null && secretKey == null) {
 			client = new AmazonS3Client(new com.amazonaws.services.s3.AmazonS3Client(config));
 		}
 		else {