Authentication Service

Janus is an authentication and identity service for Etna applications. It is based on the etna gem.

Janus implements the basic user and project structure of Etna applications.


A Janus user is primarily identified by an email address. You may add users via the bin/janus add_user command.

See below on how users may authenticate.


A ‘project’ is the entity that produced a particular data set. You may add projects using the bin/janus add_project command. Generally Etna applications communicate using the project_name and rarely The Full Name of the Project.


Users are granted specific permissions on each project. A permission consists of:

You may add permissions using the bin/janus permit command.


Janus provides identity by yielding a JSON web token (JWT). Client applications may verify this token using Janus’s public key, most likely through the Etna::Auth rack middleware.

The token format is: <header>.<params>.<signature>

Each section is a base64-encoded JSON hash. The params Janus reports are: { email, first, last, perm } - the latter encodes the user’s project permissions.


There are three ways to get a token:

Password login

The endpoint /login can be configured to display an HTML form for password entry. If successful, Janus will set a cookie with the token in the response. This endpoint is mostly useful for developers.

Shibboleth login

The /login endpoint can also be configured as a Shibboleth-protected endpoint for authentication. If successful, Janus will set a cookie with the token in the response. This endpoint is most suitable for browser applications. To use this method for authentication, set auth_method: shibboleth in the configuration.

Public-key login

Machine users who cannot use browsers can use a registered public key to generate a token.

The endpoint /api/tokens/nonce returns a cryptographic nonce. The user signs the nonce, base64-encodes the signature, and concatenates the result to the nonce.

The endpoint /api/tokens/generate returns a valid token if the Authorization header is set to the appropriate value.

The token generation api can be accessed via the etna gem, using the command etna administrate tokens generate --email your@email.id.

Here is a bash script that will successfully generate a Janus token on most systems (you need ‘openssl’, ‘wget’ and ‘base64’ utilities).


# The base URL for janus
# Your secret key file in PEM format
# Your email address
EMAIL=$(echo -n $3 | base64 -w 0)

NONCE=$(wget -q -O - $JANUS_URL/api/tokens/nonce)

SIG=$(echo -n $NONCE.$EMAIL | openssl dgst -sha256 -sign $PEM | base64 -w 0)


TOKEN=$(wget --post-data='' -q -O - --header="Authorization: Signed-Nonce $AUTH" $JANUS_URL/api/tokens/generate )

echo $TOKEN

Task tokens

Janus tokens are usually limited in lifespan as they cannot be easily invalidated. However, this makes them unsuitable for many tasks (e.g. uploading to Metis) since they may expire before the task can be completed. Therefore Janus will also issue a “task” token with a longer lifespan and limited permissions for a single project.

To acquire a task token, you may pass the argument token_type=task to the endpoint /api/tokens/generate, along with a project_name argument. Alternatively, you may use the etna gem command etna administrate token generate --email your@email.id --task --project-name your_project.

Task tokens may be generated either using a signed nonce or using a regular token.


Janus is an Etna application and puts all of its configuration into a config.yml YAML file.



    :database: janus
    :host: localhost
    :adapter: postgres
    :encoding: unicode
    :username: developer
    :password: <%= @psql_developer_password %>
    :pool: 5
    :timeout: 5000

    # We recommend using a search path that is not 'public' (for postgres only).
    :search_path: [private]

  # How Janus should generate passwords (using Etna::SignService).
  :pass_algo: sha256
  :pass_salt: <%= @janus_password_salt %>

  # Token generation options.
  :token_domain: ucsf.edu
  :token_life: 86400
  :token_algo: RS256
  :token_name: <%= @janus_token_name %>

  :log_level: debug
  :log_file: '<%= @log_file %>'

  # Janus private key (used to generate the user token).
  :rsa_private: |
<%= @rsa_private %>

  # Janus public key. This is required in the config.yml files of other
  # servers/apps that use the etna gem. We keep it here for reference.
  :rsa_public: |
<%= @rsa_public %>

Generating keys

Janus relies on a RSA public and private key pair. You may generate keys in PEM format using the command bin/janus generate_key_pair <key_size>.

User and Project Setup

Via Command line

Creating a user

You may add a new user with the add_user command. The primary identifier for a user is an email address. They may also have a first and last name. You may optionally set a password here.

Setting a public key

Some users will want to set a public key to allow them to generate a janus token via the /generate endpoint (see above). You may set this key using the add_user_key command and a public key file. Keys must be in PEM format and must be RSA keys.

To create a public / private key pair, you can use the following commands:

$ openssl genrsa -out privatekey.pem 2048
$ openssl rsa -in privatekey.pem -out publickey.pem -pubout -outform PEM

And the resulting file (publickey.pem) should look like:

-----END PUBLIC KEY-----

You can then paste that key into the Janus Settings page, in the textarea for your SSH key.

Creating a project

You may add a new project with the add_project command. The project_name is snake_cased and is the primary referrent for the project throughout Etna applications. Most Etna applications will not acknowledge a project if there is no corresponding Janus project entry.

Adding permissions

Each user has a permission for a project. You may add a permission using the permit command. Each permission consists of a role (administrator, editor, or viewer) and whether or not the user can see restricted data.

Via web portal

Project permissions may be managed for each user by browsing to JANUS_HOST/project/:project_name, e.g. https://janus.example.org/project/my_project. This page includes forms to alter roles and privileged data access for each user in your project, disable a user’s access to your project, or add a new user to the project with a given role.