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iam-role-injector

The IAM Role Injector is a tool for easily assuming an IAM Role with Multi-Factor Authentication (MFA). It manipulates environment variables to allow codebases already using AWS credentials to use IAM roles with minimal to no refactoring. In the same vein, the Role Injector can also be used to help users using the command line tools to assume a role.

Assumptions

  • AWS CLI configured correctly, storing 'aws_access_key_id' and 'aws_secret_access_key' in either environment variables -OR- in ~/.aws/credentials
  • One of the following Scenarios apply:

Scenario One: Federated AWS Accounts

  • At least two AWS Accounts:
    • AWS Account 1 must have a policy that includes sts:AssumeRole to AWS Account 2
    • AWS Account 2 must have a Trust Relationship on a role that references AWS Account 1
  • AWS Account 1 may now assume the role in AWS Account 2 that has the Trust Relationship

Scenario Two: Single AWS Account

  • An IAM User Account with a policy that include sts:Assume on an IAM Role.
  • The IAM Role has a trust relationship that allows entities in the account to assume it
  • In this case, AWS Account 1 and AWS Account 2 are the same.

Installation

  1. Install AWS CLI
  2. Configure AWS CLI with required credentials, either as Environment Variables or by running 'aws configure'
  3. Clone this repo

Increase AWS IAM Role max-session-duration

1 hour is used by default (following the AWS assume-role default), if no timeout time is specified. To update an AWS IAM role beyond 1 hour using the sts assume-role call, you must initially update the IAM role with a max-session-duration (in seconds). e.g. (for 12 hours):

aws iam update-role --role-name administrator --max-session-duration 43200

Command Line Usage

IMPORTANT NOTE: The command below starts with "source"! If you run the script without sourcing it, the environment variables will go out of scope when the script ends and you'll have a bad time.

source /path/to/sts_assume_role.sh -d [destination_account__number] -r [rolename]

e.g. source /path/to/sts_assume_role.sh -d 1234567890 -r administrator

e.g. source /path/to/sts_assume_role.sh --source 9876543210 --user iam-user --destination 1234567890 --role administrator --timeout 6h --mfa 552255

Optional features:

Help menu

/path/to/sts_assume_role.sh -h
[Help Menu Options]
Specify at least a role (-r) and destination account (-d)
    -d|--destination    to which AWS account you will assume-role
    -h|--help           (this) help menu
    -i|--info           output aws Info
    -m|--mfa            multi-factor (2fa/mfa) authentication (default is NONE)
    -r|--role           aws role you wish be become
    -s|--source         source account id (not needed if you can 'aws iam list-account-aliases')
    -t|--timeout        duration in which assume-role will be functional
                        (values in (s)econds,(m)inutes,(h)ours - 60m up to 12h. Default is 3600s)
    -u|--user           iam user name (not needed if you can 'aws sts get-caller-identity')
    -x|--unset          unset assumed role vars

Show current iam user or role info

/path/to/sts_assume_role.sh -i

Revert to iam user from role

/path/to/sts_assume_role.sh -x

Specify expiration (aws sts now supports from 1 hour, up to 12 hours)

source /path/to/sts_assume_role.sh -d [destination_account__number] -r [rolename] -t 4h works with seconds, minutes, or hours. e.g. -t 2h -t 120m -t 7200s -t 7200

Specify nothing, and you will be prompted for necessary information

source /path/to/sts_assume_role.sh
[No values set, please enter at least the destination account number and role name to assume a role]
Source Account (Default is NONE): 9876543210
Destination Account: 1234567890
IAM User Name (Default is NONE): iam-user
Role: administrator
Timeout (Default is 1h):
Multifactor Authentication? (default is NONE):

Variables exported

AWS_ACCOUNT_NAME
AWS_ACCESS_KEY_ID
AWS_ENV_VARS
AWS_SECRET_ACCESS_KEY
AWS_SESSION_TOKEN
AWS_STS_EXPIRATION
AWS_STS_TIMEOUT
AWS_USER
OG_AWS_ACCESS_KEY_ID
OG_AWS_SECRET_ACCESS_KEY

Expiration/Timeout use case

AWS_STS_EXPIRATION and AWS_STS_TIMEOUT are helpful to create a basic functions to determine how much time until the assume-role has expired.

function timeToSTSExpiration(){
  echo $(( $(( ${AWS_STS_TIMEOUT} - $(date -u +%s) )) / 60 ))
}

It can even be added to your prompt. e.g.

function checkSTS() {
if [[ -n $AWS_STS_EXPIRATION && $AWS_STS_TIMEOUT -ge $(date +%s) ]]; then
  AWS_STS_MINUTES_REMAINING=$(( $(( AWS_STS_TIMEOUT - $(date -u +%s) )) / 60 ))
  echo "$AWS_ACCOUNT_NAME|$AWS_STS_MINUTES_REMAINING"
elif [[ $AWS_STS_TIMEOUT -le $(date +%s) ]]; then
  unset AWS_STS_EXPIRATION
fi
STS_PROMPT_="$STS_COLOR"'$(checkSTS)'
PROMPT="$STS_PROMPT >"

Legacy script

source ~/assume_role.sh {sourceAccountNumber} {username} {destinationAccountNumber} {rolename}
  • sourceAccountNumber: AWS Account Number of AWS Account 1
  • username: AWS Account 1 username
  • destinationAccountNumber: AWS Account Number of AWS Account 2
  • rolename: the name of the role to assume in AWS Account 2 that has the Trust Relationship to AWS Account 1

Calling the script with 'source' is required for the environment variables to persist past the runtime of the script.

The script will also protect your original credentials if you chose to store them as environment variables.

Bugs

Please report any bugs to: https://github.com/civisanalytics/iam-role-injector/issues

Contributing

Open an issue or a pull request if you see how we can improve the script!

License

iam-role-injector is released under the BSD 3-Clause License.