Add a policy to an Amazon S3 bucket using an Amazon SDK

bool AwsDoc::S3::PutBucketPolicy(const Aws::String &bucketName,
                                 const Aws::String &policyBody,
                                 const Aws::Client::ClientConfiguration &clientConfig) {
    Aws::S3::S3Client s3_client(clientConfig);

    std::shared_ptr<Aws::StringStream> request_body =
            Aws::MakeShared<Aws::StringStream>("");
    *request_body << policyBody;

    Aws::S3::Model::PutBucketPolicyRequest request;
    request.SetBucket(bucketName);
    request.SetBody(request_body);

    Aws::S3::Model::PutBucketPolicyOutcome outcome =
            s3_client.PutBucketPolicy(request);

    if (!outcome.IsSuccess()) {
        std::cerr << "Error: PutBucketPolicy: "
                  << outcome.GetError().GetMessage() << std::endl;
    }
    else {
        std::cout << "Set the following policy body for the bucket '" <<
                  bucketName << "':" << std::endl << std::endl;
        std::cout << policyBody << std::endl;
    }

    return outcome.IsSuccess();
}


//! Build a policy JSON string.
/*!
  \sa GetPolicyString()
  \param userArn Aws user Amazon Resource Name (ARN).
      For more information, see https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_identifiers.html#identifiers-arns.
  \param bucketName Name of a bucket.
*/

Aws::String GetPolicyString(const Aws::String &userArn,
                            const Aws::String &bucketName) {
    return
            "{\n"
            "   \"Version\":\"2012-10-17\",\n"
            "   \"Statement\":[\n"
            "       {\n"
            "           \"Sid\": \"1\",\n"
            "           \"Effect\": \"Allow\",\n"
            "           \"Principal\": {\n"
            "               \"AWS\": \""
            + userArn +
            "\"\n""           },\n"
            "           \"Action\": [ \"s3:GetObject\" ],\n"
            "           \"Resource\": [ \"arn:aws:s3:::"
            + bucketName +
            "/*\" ]\n"
            "       }\n"
            "   ]\n"
            "}";
}

    public static void setPolicy(S3Client s3, String bucketName, String policyText) {

        System.out.println("Setting policy:");
        System.out.println("----");
        System.out.println(policyText);
        System.out.println("----");
        System.out.format("On Amazon S3 bucket: \"%s\"\n", bucketName);

        try {
            PutBucketPolicyRequest policyReq = PutBucketPolicyRequest.builder()
                .bucket(bucketName)
                .policy(policyText)
                .build();

            s3.putBucketPolicy(policyReq);

        } catch (S3Exception e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }

        System.out.println("Done!");
    }

    // Loads a JSON-formatted policy from a file
    public static String getBucketPolicyFromFile(String policyFile) {

        StringBuilder fileText = new StringBuilder();
        try {
            List<String> lines = Files.readAllLines(Paths.get(policyFile), StandardCharsets.UTF_8);
            for (String line : lines) {
                fileText.append(line);
            }

        } catch (IOException e) {
            System.out.format("Problem reading file: \"%s\"", policyFile);
            System.out.println(e.getMessage());
        }

        try {
            final JsonParser parser = new ObjectMapper().getFactory().createParser(fileText.toString());
            while (parser.nextToken() != null) {
            }

        } catch (IOException jpe) {
            jpe.printStackTrace();
        }
        return fileText.toString();
    }

Add the policy.

import { PutBucketPolicyCommand, S3Client } from "@aws-sdk/client-s3";

const client = new S3Client({});

export const main = async () => {
  const command = new PutBucketPolicyCommand({
    Policy: JSON.stringify({
      Version: "2012-10-17",
      Statement: [
        {
          Sid: "AllowGetObject",
          // Allow this particular user to call GetObject on any object in this bucket.
          Effect: "Allow",
          Principal: {
            AWS: "arn:aws:iam::ACCOUNT-ID:user/USERNAME",
          },
          Action: "s3:GetObject",
          Resource: "arn:aws:s3:::BUCKET-NAME/*",
        },
      ],
    }),
    // Apply the preceding policy to this bucket.
    Bucket: "BUCKET-NAME",
  });

  try {
    const response = await client.send(command);
    console.log(response);
  } catch (err) {
    console.error(err);
  }
};

class BucketWrapper:
    """Encapsulates S3 bucket actions."""
    def __init__(self, bucket):
        """
        :param bucket: A Boto3 Bucket resource. This is a high-level resource in Boto3
                       that wraps bucket actions in a class-like structure.
        """
        self.bucket = bucket
        self.name = bucket.name

    def put_policy(self, policy):
        """
        Apply a security policy to the bucket. Policies control users' ability
        to perform specific actions, such as listing the objects in the bucket.

        :param policy: The policy to apply to the bucket.
        """
        try:
            self.bucket.Policy().put(Policy=json.dumps(policy))
            logger.info("Put policy %s for bucket '%s'.", policy, self.bucket.name)
        except ClientError:
            logger.exception("Couldn't apply policy to bucket '%s'.", self.bucket.name)
            raise

# Wraps an Amazon S3 bucket policy.
class BucketPolicyWrapper
  attr_reader :bucket_policy

  # @param bucket_policy [Aws::S3::BucketPolicy] A bucket policy object configured with an existing bucket.
  def initialize(bucket_policy)
    @bucket_policy = bucket_policy
  end

  # Sets a policy on a bucket.
  #
  def set_policy(policy)
    @bucket_policy.put(policy: policy)
    true
  rescue Aws::Errors::ServiceError => e
    puts "Couldn't set the policy for #{@bucket_policy.bucket.name}. Here's why: #{e.message}"
    false
  end

end