AWS sts assume role in one command

Question

To assume an AWS role in the CLI, I do the following command:

aws sts assume-role --role-arn arn:aws:iam::123456789123:role/myAwesomeRole --role-session-name test --region eu-central-1

This gives to me an output that follows the schema:

{
    "Credentials": {
        "AccessKeyId": "someAccessKeyId",
        "SecretAccessKey": "someSecretAccessKey",
        "SessionToken": "someSessionToken",
        "Expiration": "2020-08-04T06:52:13+00:00"
    },
    "AssumedRoleUser": {
        "AssumedRoleId": "idOfTheAssummedRole",
        "Arn": "theARNOfTheRoleIWantToAssume"
    }
}

And then I manually copy and paste the values of AccessKeyId, SecretAccessKey and SessionToken in a bunch of exports like this:

export AWS_ACCESS_KEY_ID="someAccessKeyId"                                                                                      
export AWS_SECRET_ACCESS_KEY="someSecretAccessKey"
export AWS_SESSION_TOKEN="someSessionToken"

To finally assume the role.

How can I do this in one go? I mean, without that manual intervention of copying and pasting the output of the aws sts ... command on the exports.

Solution 1

Finally, a colleague shared with me this awesome snippet that gets the work done in one go:

eval $(aws sts assume-role --role-arn arn:aws:iam::123456789123:role/myAwesomeRole --role-session-name test | jq -r '.Credentials | "export AWS_ACCESS_KEY_ID=\(.AccessKeyId)\nexport AWS_SECRET_ACCESS_KEY=\(.SecretAccessKey)\nexport AWS_SESSION_TOKEN=\(.SessionToken)\n"')

Apart from the AWS CLI, it only requires jq which is usually installed in any Linux Desktop.

Solution 2

No jq, no eval, no multiple exports - using the printf built-in (i.e. no credential leakage through /proc) and command substitution:

export $(printf "AWS_ACCESS_KEY_ID=%s AWS_SECRET_ACCESS_KEY=%s AWS_SESSION_TOKEN=%s" \
$(aws sts assume-role \
--role-arn arn:aws:iam::123456789012:role/MyAssumedRole \
--role-session-name MySessionName \
--query "Credentials.[AccessKeyId,SecretAccessKey,SessionToken]" \
--output text))

Solution 3

You can store an IAM Role as a profile in the AWS CLI and it will automatically assume the role for you.

Here is an example from Using an IAM role in the AWS CLI - AWS Command Line Interface:

[profile marketingadmin]
role_arn = arn:aws:iam::123456789012:role/marketingadminrole
source_profile = user1

This is saying:

• If a user specifies --profile marketingadmin
• Then use the credentials of profile user1
• To call AssumeRole on the specified role

This means you can simply call a command like this and it will assume the role and use the returned credentials automatically:

aws s3 ls --profile marketingadmin

Solution 4

Arcones's answer is good but here's a way that doesn't require jq:

eval $(aws sts assume-role \
 --role-arn arn:aws:iam::012345678901:role/TrustedThirdParty \
 --role-session-name=test \
 --query 'join(``, [`export `, `AWS_ACCESS_KEY_ID=`, 
 Credentials.AccessKeyId, ` ; export `, `AWS_SECRET_ACCESS_KEY=`,
 Credentials.SecretAccessKey, `; export `, `AWS_SESSION_TOKEN=`,
 Credentials.SessionToken])' \
 --output text)

Solution 5

I have had the same problem and I managed using one of the runtimes that the CLI served me.

Once obtained the credentials I used this approach, even if not so much elegant (I used PHP runtime, but you could use what you have available in your CLI):

- export AWS_ACCESS_KEY_ID=`php -r 'echo json_decode(file_get_contents("credentials.json"))->Credentials->AccessKeyId;'`
- export AWS_SECRET_ACCESS_KEY=`php -r 'echo json_decode(file_get_contents("credentials.json"))->Credentials->SecretAccessKey;'`
- export AWS_SESSION_TOKEN=`php -r 'echo json_decode(file_get_contents("credentials.json"))->Credentials->SessionToken;'`

where credentials.json is the output of the assumed role:

aws sts assume-role --role-arn "arn-of-the-role" --role-session-name "arbitrary-session-name" > credentials.json

Obviously this is just an approach, particularly helping in case of you are automating the process. It worked to me, but I don't know if it's the best. For sure not the most linear.

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