Vault CircleCI Authentication Plugin

This plugin allows a running CircleCI build to authenticate itself with a Vault server in order to obtain a Vault token associated with policies mapped to the given CircleCI project.

Architecture

The authentication is achieved by providing details about the running CircleCI build that the Vault server can verify using the CircleCI API.

Configuration

The plugin must be configured with certain parameters prior to being able to successfully handle login requests. The plugin is configured by sending a POST request to the auth/circleci/config endpoint.

Request parameters:

• circleci_token is a CircleCI personal API token that allows the plugin to make API calls to CircleCI.

• base_url (optional) is an alternate base URL where CircleCI API calls are sent. This parameter must end up with a slash. Defaults to https://circleci.com/api/v1.1/.

• vcs_type is a value indicating the Version Control System type of the project builds being looked up in CircleCI's API. Valid values are github and bitbucket.

• owner is the username or organization that owns the project in the VCS.

• ttl is a time duration used as the default ttl when no ttl is specified with the login request. This value is larger than max_ttl, it will be capped at max_ttl.

• max_ttl is a time duration that sets the largest ttl that a new token can be assigned in this plugin.

• attempt_cache_expiry is the time duration that the backend caches login attempts. Defaults to 18000s (5 hours).

The plugin caches login attempts for and an approximate duration of attempts_cache_time. The longer this duration, the greater the memory requirement will be. However, in order to prevent replay attacks, the plugin must cache the attempt for a duration that exceeds the maximum CircleCI build duration possible.

Policy Mapping

By default, this plugin doesn't associate any policies with the tokens that it creates, except for the default policy. To specify which policies are associated, a mapping of project to policies must be provided by sending a POST request to the auth/circleci/map/projects/:project endpoint.

Request parameters:

• project is the name of the CircleCI project being mapped to specific policies.

• value is a comma separated list of policy names to map to the specified project.

Authentication

To create a token with this plugin, send a POST request to the auth/circleci/login endpoint.

Request parameters:

• project is the name of the CircleCI project.

• build_num is the number of the running CircleCI build.

• vcs_revision is the VCS revision (commit hash) of the code which triggered the current build.

Upon receiving this request, the Vault server will serve it to this plugin, which in turn will initiate a GET request to :base_url/project/:vcs_type/:owner/:project/:build_num?circle-token=:circleci_token

Request parameters:

• vcs_type is the type of Version Control System for this project as specified in the plugin's configuration.

• owner is the user or organization that owns this project as specified in the plugin's configuration.

• project is the name of the CircleCI project as specified in the Login request.

• build_num is the number of the current CircleCI build as specified in the Login request.

• circleci_token is a CircleCI personal API token that gives access to the project/ endpoint as specified in the plugin's configuration.

CircleCI will respond to this request with a response describing the specified build.

{
  "vcs_url" : ...,
  "build_url" : ...,
  "build_num" : :build_num,
  "branch" : ...,
  "vcs_revision" : ":hash",
  "committer_name" : ...,
  "committer_email" : ...,
  "subject" : ...,
  "body" : ..., 
  "why" : ...,
  "dont_build" : ...,
  "queued_at" : ...,
  "start_time" : ...,
  "stop_time" : ...,
  "build_time_millis" : ...,
  "username" : ":user",
  "reponame" : ":project",
  "lifecycle" : "running",
  "outcome" : ...,
  "status" : "running",
  "retry_of" : ...,
  "steps" : [ ... ],
  ...
}

The plugin will verify that both the lifecycle key in the response is set to running, and that the vcs_revision key is set to the same value as the vcs_revision parameter that was specified in the Login request. If these conditions are met, a new token will be created with all of the mapped policies associated to it, in addition to the default policy.

Finally the plugin will send a response to the initial Login request that resembles the following:

{
    "auth": {
        "client_token": "00000000-1111-2222-3333-444444444444",
        "policies": [
            "default",
            "mapped-policy"
        ],
        "metadata": {
        },
        "lease_duration": 300,
        "renewable": false
    }
}