Multiple IdP Support

[jrchamp]

Need to be able to configure multiple IdP options. The initial version of this may only require a restructure of the General tab's settings.

Global plugin settings:

• Attribute Access (no change needed, the Shibboleth mappings should populate the same variables)
• Default Login Method (this might switch from a checkbox to a select of {wp-login/User Choice, IdP 1, IdP2})
• Automatic Login (no change needed, same logic as Attribute Access)
• Disable Local Authentication (no change needed)
• Login URL (local URL, typically /Shibboleth.sso/Login)
• Logout URL (local URL, typically /Shibboleth.sso/Logout?redirect=<website home>)

Per-IdP settings:

• New field: entityId (so we know which IdP they want to use)
• New field: IdP short code (a couple letters so that we can provide direct links)
• Password Change URL (for us to use this, we need to know which IdP the user is from)
• Password Reset URL (for us to use this, we need to know which IdP the user is from)
• Button Text (this will allow the user to differentiate between IdPs)

Other changes needed:

• The user meta key shibboleth_account currently has a value of true. This may be an excellent place for us to store a short identifier like campus or c that has been configured as the short identifier for the configured IdPs.
• The upgrade step would probably need to automatically assign a default identifier, such as default and update all of the existing meta keys so that it matches.
• The identifier field should not be easy to accidentally edit. If we do allow updating that identifier value, we should also update the associated users to the new identifier.
• When this identifier exists, if we receive a login request that provides the desired IdP identifier, we can automatically direct the user to the specified Login URL.

[smbader]

Administration:

• [x] Add a new tab to Shibboleth settings "Manage IdPs" with the following:
• [x] A table of all used IdPs (with edit / delete options)
• [x] A "Create New IdP" button
• [x] Create / edit form allows configuration of "Per-IdP" settings listed above

[smbader]

Front-End:

• [x] Display a button for each configured IdP

[smbader]

Back-End:

• [x] On startup or install, convert old values to the new format (idp array values). This would take old values and insert them as the first idp in the array.
• [x] Update shibboleth account "true" values to "default"