mercredi 14 juin 2023

Zsh function to assume a role in AWS

Working in AWS, I sometimes need to test a role to debug some issues or validate some hypotheses.

I'm already using the Granted CLI to assume federated roles in the AWS accounts I have access to, but it doesn't let me quickly change role (either in the same AWS account or in another one).

I wrote a small Zsh function to make this possible.


Autoload functions in .zshrc

Add these lines inside your .zshrc:

fpath=(~/.zfunctions $fpath)
autoload -Uz ${fpath[1]}/*(:t)

Zsh function: role-assume

Write the following to the file ~/.zfunctions/role-assume

#!/usr/bin/env zsh

# Script to assume a role using AWS CLI
# Dependencies : jq

role-assume () {

  if [[ -z "$1" ]]; then
    echo "You need to pass the role ARN as an argument to this function, like this: role-assume \"arn:aws:iam::123456789000:role/role-name\""

  OUT=$(aws sts assume-role --role-arn $1 --role-session-name assume-role-local-func --output json);\
  export AWS_ACCESS_KEY_ID=$(echo $OUT | jq -r '.Credentials''.AccessKeyId');\
  export AWS_SECRET_ACCESS_KEY=$(echo $OUT | jq -r '.Credentials''.SecretAccessKey');\
  export AWS_SESSION_TOKEN=$(echo $OUT | jq -r '.Credentials''.SessionToken');

  echo "Trying 'aws sts get-caller-identity'";
  echo $(aws sts get-caller-identity | jq -r '.UserId' )


Open a new shell. You should now be able to assume a role by passing the ARN to the function.

# use granted `assume` cli app to get the initial credentials

assume account-role-x

# [✔] [account-role-x](ca-central-1) session credentials will expire in 8 hours

# call the function with a role ARN

role-assume arn:aws:iam::role-y-other-account

Trying 'aws sts get-caller-identity'

The function is outputting the userId returned by aws sts get-caller-identity to confirm that we now have the new credentials.

Obviously, the trust policy in the role you want to assume must allow the initial role/user to allow sts:AssumeRole. Such as:

  "Version": "2012-10-17",
  "Statement": [
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::111122223333:role/account-role-x"
      "Action": "sts:AssumeRole"