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A kerberos implementation of an STS client leveraging ADFS and Kerberos. This project was inspired by https://blogs.aws.amazon.com/security/post/Tx1LDN0UBGJJ26Q/How-to-Implement-Federated-API-and-CLI-Access-Using-SAML-2-0-and-AD-FS
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README.md

AWS KERBEROS STS

Based on the ADFS-CLI script originally posted by Quint Van Deman.

Overview

This script provides a seamless mechanism for federating the AWS CLI. When properly configured, this script allows a user to get a short lived (1 hour) set of credentials for each authorized role.

The script leverages Kerberos and a SAML-compatible IdP to avoid any need for the user to enter an AD domain password, or provide AWS credentials. However, users can also authenticate using NTLM with their username and password or with a Kerberos keytab.

See our security policy for handling of security-related matters.

Configuration

Kerb-STS looks for configuration in the ~/.kerb-sts/config.json file. This file contains the following fields:

Field Required? Description
idp_url Yes URL where the SAML authentication requests are sent
adfs_url No deprecated URL where the SAML authentication requests are sent
region Yes Region for AWS credentials
kerb_domain No Domain name used for the Kerberos GSS exchange. This is set to the domain name of idp_url by default
preferred_auth_type No Type of authentication to use when a username and password is submitted. Acceptable values: ntlm (default), kerberos

Users can generate this file with Kerb-STS:

kerb-sts --configure

This will prompt the user for those values and then serialize the configuration. Users can also manually create the configuration file. A sample for AD FS is demonstrated below:

{
  "region": "us-east-1",
  "idp_url": "https://sample.domain.com/adfs/ls/IdpInitiatedSignOn.aspx?loginToRp=urn:amazon:webservices"
}

Users can override either of the configured values on the command line.

Installation

  • Note: Python 2.7.10 is the minimal version supported
  • Note: All platforms have been tested with both Python 2.7 and 3.5

OSX

  • Note: If you are using El Capitan or Sierra, refer to the subsequent OSX section
  1. sudo easy_install pip
  2. sudo pip install kerb-sts

OSX - El Capitan

  • Note: El Capitan forces the version of some modules which directly interfere with kerb-sts. In order to get it to work users need to either use a version of Python that was not included with the OS or need to follow these instructions which leverage virtual environments.
  1. sudo easy_install pip virtualenv
  2. virtualenv ~/kerb-sts
  3. source ~/kerb-sts/bin/activate
  4. sudo pip install kerb-sts --ignore-installed six
  5. deactivate
  6. sudo ln -s ~/kerb-sts/bin/kerb-sts /usr/local/bin/kerb-sts

MacOS Sierra

  1. You will need to update your version of Python to 2.7.12+; Homebrew is the easiest method.
  2. You will also need to install/update the XCODE Development Extensions 1a. sudo xcode-select install
  3. You can then just run sudo pip install kerb-sts

Windows

  1. Install Python
  2. Ensure python and python/scripts are on the PATH
  3. Install pywin32 from mhammond/pywin32. Follow the instructions to ensure you get the correct version.
  4. pip install kerb-sts

Ubuntu

  1. sudo apt-get update
  2. sudo apt-get install -y krb5-kdc libkrb5-dev python-setuptools python3-pip
  3. sudo pip install kerb-sts

Usage

If the install went smoothly kerb-sts should be on your path. There are a lot of configuration options. The best way to discover them is to check out the help statement.

kerb-sts --help

Default Role

The script allows users to specify an AWS IAM role that will be set as the default IAM role in the credentials file.

kerb-sts -r [iam-role-to-assume]

All subsequent AWS CLI commands will use this role by default.

Additionally, all available roles will be added as named profiles to the credentials file. Users can then leverage the default role or use the AWS_DEFAULT_PROFILE environment variable to select a specific role/profile. You can find more information about the credentials file in the AWS Documentation.

Only Role

If you have a lot of roles available, it may take a while to process all available roles. In this case, you can use the -o option and only the specified role will be processed. It will also be treated as the default role (-r option).

Daemon

By passing in a --daemon flag, the script will continue running and update the credentials file every half hour. The refresh time can be set with the --refresh argument, but remember the tokens only last for one hour.

kerb-sts -r iam-role-to-assume --daemon

Authenticating with Username/Password

kerb-sts -u username -p 'password' -d DOMAIN

Based on the value of preferred_auth_type in your config file, this call with authenticate using NTLM, or will create a kerberos ticket for the inputted user and authenticate.

Keytab

This script allows users to generate Kerberos tokens with Kerberos keytabs. Keytabs are private key files that are signed with the user's name, domain, and password. You can generate a keytab by running:

ktutil -k username.keytab add -p username@DOMAIN.COM -e arcfour-hmac-md5 -V 1

Users can use the keytab to authenticate with Kerberos by running:

kinit -kt username.keytab username@DOMAIN.COM

Keytabs allow users to authenticate without their password. The keytab is signed with the password however, so when a password is updated the keytab must likewise be updated. They can then be used with kerb-sts to generate temporary tokens:

kerb-sts --key username.keytab -u username -d DOMAIN.COM

Credential File

The default location for the AWS credentials file is ~/.aws/credentials. Users are also able to specify a different location for the credentials generated.

kerb-sts -c ./aws-credentials

Troubleshooting

Kerberos

If you are having issues authenticating with Kerberos, make sure you can run kinit. This should prompt you for your password and then login successfully. You can view your current Kerberos tickets with klist. If you want to ensure Kerberos is working properly you can delete all of your tickets with kdestroy -A and then try to get another ticket issued by running kinit.

Building a Distribution

Python

The easiest way to install and distribute kerb-sts is using a wheel. A distribution can be built by running:

python setup.py bdist_wheel

That should output a .whl file in the dist directory which can be installed with pip.

Windows EXE

Kerb-STS can also be built into a standalone executable with Python bundled to ease installation.

python setup.py install
pip install pyinstaller
pyinstaller --onfile kerb_sts/__main__.py

This will produce a dist/__main__.exe which can then be renamed/run as a standalone exe.

Development

The recommended way to install locally from source is to use a virtual environment. From the root of the kerb-sts source code directory run:

  1. pip install virtualenv
  2. virtualenv venv
  3. source venv/bin/activate
  4. python setup.py install
  5. python kerb_sts/
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