Resolves issue #6788
The AuthenticationMethed is passed in via hidden field as per usual, but due to changes, the fallback authenticator was always the MemberAuthenticator and the actual passed in authenticator was defaulting to an empty string.
This causes an issue when there are multiple authenticators and the default authenticator is _not_ in the allowed authenticators, but is still the default. It caused the getAuthenticator method to return the default MemberAuthenticator to be returned, despite it being disabled.
A second issue around multiple authenticators, was the template using a no-longer used method `getAuthenticatorName`. This method returned a null on the default MemberLoginForm (as nothing was set), causing a Warning.
Because the getAuthenticator and getAuthenticatorName are no longer in
use, I've opted to replace these with a translatable string
`getAuthenticatorName`, to
display the title of the form on the tabs, as per the tabset on
Security_MultiAuthenticatorLogin template.
API Add HasRequestHandler interface
API Refactor Link() and url handling behaviour from Controller into RequestHandler
API RequestHandler classes now must define url_segment to have a default Link()
API Clean up redirectBack()
* Introduced in 0cf477d36
* Should use the "template_main" static to decide which model to use for rendering this page
* Assuming SiteTree means any requirements added in Page and assumed to work everywhere will not
Aaron Carlino
Simon Erkelens
Damian Mooyman
Daniel Hensby
Robbie Averill
Mike Cochrane
Sam Minnee