AWS STS: GetFederationToken works locally, but fails from Lambda

Question

I'm trying to call generate a temporary token via STS, using the aws-sdk (Typescript). This is the code which tries to obtain the token.

export async function handler() {
  const token = await sts
    .getFederationToken({
      DurationSeconds: 7200,
      Name: "test",
      Policy: JSON.stringify({
        Version: "2012-10-17",
        Statement: {
          Effect: "Allow",
          Action: "ses:*",
          Resource: "*",
        },
      }),
    })
    .promise();
}

Executing it locally works. Deploying it to a Lambda and running it yields the following error:

{
  "errorType": "AccessDenied",
  "errorMessage": "Cannot call GetFederationToken with session credentials",
  "trace": [
    "AccessDenied: Cannot call GetFederationToken with session credentials",
    "    at Request.extractError (/var/runtime/node_modules/aws-sdk/lib/protocol/query.js:50:29)",
    "    at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:106:20)",
    "    at Request.emit (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:78:10)",
    "    at Request.emit (/var/runtime/node_modules/aws-sdk/lib/request.js:686:14)",
    "    at Request.transition (/var/runtime/node_modules/aws-sdk/lib/request.js:22:10)",
    "    at AcceptorStateMachine.runTo (/var/runtime/node_modules/aws-sdk/lib/state_machine.js:14:12)",
    "    at /var/runtime/node_modules/aws-sdk/lib/state_machine.js:26:10",
    "    at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:38:9)",
    "    at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:688:12)",
    "    at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:116:18)"
  ]
}

I am fairly certain the function has all the rights that are necessary (sts:*, ses:*, ...). Do Lambdas generally run in a context where getFederationToken is not permitted?

score 0 · Answer 1 · answered May 20 '22 at 05:32

I just ran into the same problem.... I understand that Lambda get's it's role via AssumeRole, which if we look at the STS API Comparison it says

Cannot call GetFederationToken or GetSessionToken.

And if we continue to look it appears no such api is able to call those API's (Being an STS operation)

The only workaround I can figure is to create an IAM user, and use it's API keys directly (Stored securely, perhaps in Secrets Manager)

AWS STS: GetFederationToken works locally, but fails from Lambda

1 Answers1