VaultSharp/Lobby

Hi, im trying to login using AWS IAM, but stuck with an exception:

{"errors":["didn't supply required authentication values"]}

code (copied from GitHub's README page):

           var amazonSecurityTokenServiceConfig = new AmazonSecurityTokenServiceConfig();
            var creds = FallbackCredentialsFactory.GetCredentials();
            var iamRequest = GetCallerIdentityRequestMarshaller.Instance.Marshall(new GetCallerIdentityRequest());
            iamRequest.Endpoint = new Uri(amazonSecurityTokenServiceConfig.DetermineServiceURL());
            iamRequest.ResourcePath = "/";
            iamRequest.Headers.Add("User-Agent", "https://github.com/rajanadar/vaultsharp/0.11.1000");
            iamRequest.Headers.Add("X-Amz-Security-Token", creds.GetCredentials().Token);
            iamRequest.Headers.Add("Content-Type", "application/x-www-form-urlencoded; charset=utf-8");
            new AWS4Signer().Sign(iamRequest, amazonSecurityTokenServiceConfig, new RequestMetrics(), creds.GetCredentials().AccessKey, 
                 creds.GetCredentials().SecretKey);
            var iamStsRequestHeaders = iamRequest.Headers;
            var base64EncodedIamRequestHeaders = Convert.ToBase64String(Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(iamStsRequestHeaders)));

            var a1 = new IAMAWSAuthMethodInfo(AuthMethodType.AWS.Type, base64EncodedIamRequestHeaders, Guid.NewGuid().ToString(), "mt-fxrates-honduras");
            var cs = new VaultClientSettings(settings.Vault.Host, a1);
            var c = new VaultClient(cs);
            var secret = c.V1.Secrets.KeyValue.V1.ReadSecretAsync(settings.Vault.Path).Result;

vault's role record

vault write auth/aws/role/mt-fxrates-honduras auth_type=iam policies=mt-fxrates-honduras max_ttl=1h bound_iam_principal_arn=arn:aws:iam::312226949769:role/lambda_basic_vpc_execution

Any help is appreciated. Thanks