Amazon.Runtime.AWSCredentials.GetCredentials C# (CSharp) Method

        public abstract ImmutableCredentials GetCredentials();
    }

        /// <summary>
        ///  Given a policy and AWS credentials, produce a S3PostUploadSignedPolicy.
        /// </summary>
        /// <param name="policy">JSON string representing the policy to sign</param>
        /// <param name="credentials">Credentials to sign the policy with</param>
        /// <returns></returns>
        public static S3PostUploadSignedPolicy GetSignedPolicy(string policy, AWSCredentials credentials)
        {
            var policyBytes = Encoding.UTF8.GetBytes(policy.Trim());
            var base64Policy = Convert.ToBase64String(policyBytes);
            
            string signature = null;

            signature = CryptoUtilFactory.CryptoInstance.HMACSign(Encoding.UTF8.GetBytes(base64Policy), credentials.GetCredentials().SecretKey, SigningAlgorithm.HmacSHA1);

            return new S3PostUploadSignedPolicy
            {
                Policy = base64Policy,
                Signature = signature,
                AccessKeyId = credentials.GetCredentials().AccessKey
            };
        }