AWS Assume Role via .Net SDK gives Access Denied but works with CLI - amazon-web-services

Question

I am trying to upload a file in S3 by AWS Assume Role. When I am trying to access it from CLI it works fine but from .Net SDK it gives me Access Denied error.
Here are the steps I followed in CLI -
Setup the access key/secret key for user using aws configure
Assume the Role - “aws sts assume-role --role-arn "arn:aws:iam::1010101010:role/Test-Account-Role" --role-session-name AWSCLI-Session”
Take the access key / secret key / session token from the assumed role and setup an AWS profile. The credentials are printed out/returned from the assumed role.
Switch to the assume role profile: “set AWS_PROFILE=”
Verify that the user has the role: “aws sts get-caller-identity”
Access the bucket using ls or cp or rm command - Works Successfully.
Now I am trying to access it from .Net core App -
Here is the code snippet- Note that I am using same Access and Secret key as CLI from my local.
try
{
var region = RegionEndpoint.GetBySystemName(awsRegion);
SessionAWSCredentials tempCredentials = await GetTemporaryCredentialsAsync(awsAccessKey, awsSecretKey, region, roleARN);
//Use the temp credentials received to create the new client
IAmazonS3 client = new AmazonS3Client(tempCredentials, region);
TransferUtility utility = new TransferUtility(client);
// making a TransferUtilityUploadRequest instance
TransferUtilityUploadRequest request = new TransferUtilityUploadRequest
{
BucketName = bucketName,
Key = $"{subFolder}/{fileName}",
FilePath = localFilePath
utility.Upload(request); //transfer
fileUploadedSuccessfully = true;
}
catch (AmazonS3Exception ex)
{
// HandleException
}
catch (Exception ex)
{
// HandleException
}
The method to get temp credentials is as follow - GetTemporaryCredentialsAsync
private static async Task<SessionAWSCredentials> GetTemporaryCredentialsAsync(string awsAccessKey, string awsSecretKey, RegionEndpoint region, string roleARN)
{
using (var stsClient = new AmazonSecurityTokenServiceClient(awsAccessKey, awsSecretKey, region))
{
var getSessionTokenRequest = new GetSessionTokenRequest
{
DurationSeconds = 7200
};
await stsClient.AssumeRoleAsync(
new AssumeRoleRequest()
{
RoleArn = roleARN,
RoleSessionName = "mySession"
});
GetSessionTokenResponse sessionTokenResponse =
await stsClient.GetSessionTokenAsync(getSessionTokenRequest);
Credentials credentials = sessionTokenResponse.Credentials;
var sessionCredentials =
new SessionAWSCredentials(credentials.AccessKeyId,
credentials.SecretAccessKey,
credentials.SessionToken);
return sessionCredentials;
}
}
I am getting back the temp credentials but it gives me Access Denied while uploading the file. Not sure if I am missing anything here.
Also noted that the token generated via SDK is shorter than that from CLI. I tried pasting these temp credentials to local profile and then tried to access the bucket and getting the Access Denied error then too.

Answer 1

There is an AWS .NET V3 example that shows this exact use case. To assume a role, you use a AmazonSecurityTokenServiceClient. In this example, the user assumes the role that allows the role to be used to list all S3 buckets. See this .NET scenario here.
https://github.com/awsdocs/aws-doc-sdk-examples/blob/main/dotnetv3/IAM/IAM_Basics_Scenario/IAM_Basics_Scenario/IAM_Basics.cs