Provide login hook, phpcs linting

[jules0x]

When using MFA along with this module, SAML users were not able to modify their MFA without first entering a CMS password.
As a SAML user, this is unknown/not set, so we added an extension to use this hook and call the getSudoModeService() function on SudoModeController (part of silverstripe/security-extensions module).

[madmatt]

Sorry for the massive delay! This looks good to me, and it doesn't change anything beyond adding a hook in so is API neutral.

@jules0x Do you reckon you could add some docs to describe your use case? It may not be too common to require MFA as well as SAML (typically MFA should be implemented at the IdP end, not on the SP website - as it's part of the authentication process). In any case, it would be good to know what you did so others can replicate it if they see a security benefit in doing so.

If you don't have time, let me know and I can merge this and look into it later myself.