feature: connected accounts with LDAP, OAuth, SAML

[greenpau]

A clear and concise description of what you want the system to do.

Scenarios

1. A locally-authenticated user browses to "Connected Accounts" tab in "Portal Settings".
   There, the user may click a button to associate OAuth account (Google, Facebook, etc.) with the local user account.
2. A user signs in with OAuth and lands on "portal" page. There, the user has an option to create an account in local user database.

In local database, add a list of maps.

• For LDAP, add realm and dn fields
• For OAuth, add provider and id fields

Question with OAuth:

1. what is the id associated with a provider
2. local the user in local database. requires editing go-identity