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.

Prerequisites #

• AWS CLI installed
• Granted CLI app installed and set up
• A directory to store your Zsh functions (in my case, ~/.zfunctions)
• .zshrc configured to autoload functions from that directory

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

```zsh
#!/usr/bin/env zsh

role-assume() {
  if [[ -z "$1" ]]; then
    echo "Usage: role-assume <role-arn>"
    echo "Example: role-assume \"arn:aws:iam::123456789000:role/role-name\""
    exit 1
  fi

  local out
  if ! out=$(aws sts assume-role --role-arn "$1" --role-session-name assume-role-local-func --output json); then
    echo "Failed to assume role" >&2
    exit 1
  fi

  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'"
  aws sts get-caller-identity | jq -r '.UserId'
}

### Testing

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 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'
ABCDREEEEWWWWKBKB:role-y-other-account

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"
}
]
}