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Go client to negotiate BLESS SSH certificates
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edulop91 and czimergebot [fix] Change cert file permissions to 0400 (#140)
[fix] Change cert file permissions to 0400fixes #134
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README.md

blessclient

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Please note: If you believe you have found a security issue, please responsibly disclose by contacting us at security@chanzuckerberg.com.


Inspiration for this project comes from lyft/python-blessclient. We decided to write in Go because it is much easier to distribute a statically linked binary to a large team than having to deal with python environments. Some features from lyft/python-blessclient are currently missing but will be added over time while others are purposefully excluded.

Install

Mac

You can use homebrew -

brew tap chanzuckerberg/tap
brew install blessclient

Linux

Binaries are available on the releases page. Download one for your architecture, put it in your path and make it executable.

You might also need to install libusb-dev. For ubuntu you can install libusb-1.0-0-dev.

Usage

At a high level:

  1. Install blessclient
  2. If you don't have an SSH key, generate one with ssh-keygen -t rsa -b 4096
  3. Import or generate a blessclient config. You can find an example config here.
  4. Run blessclient run and make sure there are no errors
  5. Modify your ssh config to be bless compatible
  6. ssh, scp, rsync as you normally would

Config

By default, blessclient looks for configs in ~/.blessclient/config.yml. You can always override this blessclient run -c /my/new/config.yml Some more information on the config can be found here.

There is a built-in method to facilitate the generation of blessclient configs:

Import-config

A few options here:

  • blessclient import-config git@github.com:/..../teamA/blessconfig.yml
  • blessclient import-config https://www.github.com/..../teamA/blessconfig.yml
  • blessclient import-config /home/user/.../teamA/blessconfig.yml
  • blessclient import-config s3::https://s3.amazonaws.com/bucket/teamA/blessconfig.yml

This command uses go-getter to fetch a config and thus supports any source that go-getter supports.

You can see an example config with dummy values here. Download the example, modify the values, and blessclient import-config <path> it to get started.

ssh-agent

You can optionally instruct blessclient to update your ssh-agent with your certificate. To do so, add update_ssh_agent: true to your blessclient config.

client_config:
  update_ssh_agent: true
...

.ssh/config

This is the nice part about blessclient - in general, you can write an ssh config to transparently use blessclient. scp, rsync, etc should all be compatible!

Such an ssh config could look like:

Match OriginalHost bastion.foo.com exec "blessclient run"
  IdentityFile ~/.ssh/id_rsa

Host 10.0.*
  ProxyJump bastion.foo.com
  User admin

Host bastion.foo.com
  User admin

This ssh config does a couple of interesting things -

  • It transparently requests an ssh certificate if needed
  • It transparently does a ProxyJump through a bastion host (assuming 10.0.* is an ipblock for machines behind the bastion)

Enable Okta SSO

By default, blessclient uses your IAM user credentials. Blessclient is able to support Okta SAML auth if this is enabled for your AWS account. The example config shows the configuration options available under okta_config. Blessclient uses the aws-okta library for authentication, which supports multiple MFA options.

You will need to setup a profile in your ~/.aws/config that can be accepted by aws-okta. Example configs are available here.

Telemetry

There currently is some basic trace instrumentation using honeycomb. We use this internally to track usage, gather performance statistics, and error reporting. Telemetry is disabled without a honeycomb write key - which you must provide through the config.

Common Errors

Unsafe RSA public key

Bless lambda is rejecting your key because because it is not cryptographically sound. You can generate a new key ssh-keygen -t rsa -b 4096 and use that instead.

SSH client 7.8 can't connect with certificates

There are a couple of outstanding bugs related to openSSH client 7.8

You can check your version with

ssh -V

Other

Deploying BLESS

There are already several great guides on how to run a BLESS lambda. If you take a moment to skim through these, you'll notice that setting up a successful BLESS deployment requires thorough knowledge of AWS Lambda and IAM. Even then, you'll probably spend hours digging through CloudWatch logs (and who likes doing that).

To further simplify this process, we've put together a terraform provider and module to automate BLESS deployments.

Enabling shell completion

bash

Linux
# Might need to install bash-completion on CentOS
yum install bash-completion
# install completion
echo "source <(blessclient completion bash)" >> ~/.bashrc
Mac
## If running Bash 3.2 included with macOS
brew install bash-completion
## or, if running Bash 4.1+
brew install bash-completion@2

# install completion
blessclient completion bash > $(brew --prefix)/etc/bash_completion.d/blessclient

zsh

You can add the file generated by blessclient completion zsh to a directory in your $fpath.

Contributing

Contributions and ideas are welcome! Please don't hesitate to open an issue, join our gitter chat room, or send a pull request.

Go version >= 1.12 required.

This project is governed under the Contributor Covenant code of conduct.

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