Add /whoami API endpoint

[micahlee]

When setting up network based authentication (with restricted_to) or debugging IP address issues with authentication and audit, it is helpful to observe how Conjur views your API request.

To make this more observable, we should add a new API endpoint /whoami to return the following properties of the request:

• client_ip: The rails request.ip attribute. This is used for network restrictions and audit. This can contain an unexpected value if load balancers or reverse proxies are not properly configured.

• user_agent: The rails request.user_agent attribute.

• account: The account attribute of the access token (if provided on the request, null otherwise).

• login: The login (username) attribute of the access token (if provided on the request, null otherwise).

• token_issued_at: The issued timestamp (iat) when the access token was created (if provided on the request, null otherwise).

DoD:

• API endpoint exists
• API endpoint is tested in CI
• API endpoint is documented