TYPO3 Core

The implementation of this option is quite easy. I found the solution and some example code in the German Typo3 mailinglist offered by Steffen Ritter, siehe hier:
http://www.mail-archive.com/typo3-german@lists.typo3.org/msg10697.html
I've tested it. And it works fine. Please find the auth service class class.tx_rsmysherpasusers_authservice.php attached. In addition the service has to be registered in the ext_localconf.php by:

t3lib_extMgm::addService(
'rsmysherpasusers',
'auth',
'tx_rsmysherpasusers_authservice',
array(
'title' => 'FE-Authentification via eMail',
'description' => 'looks up given username in email field instead of username field',
'subtype' => 'getUserFE',
'available' => TRUE,
'priority' => 95, // must be higher than tx_sv_auth (50) and rsaauth (60) but lower than OpenID (75) if you want to use OpenID too
'quality' => 70,
'os' => '',
'exec' => '',
'classFile' => t3lib_extMgm::extPath('rsmysherpasusers').'class.tx_rsmysherpasusers_authservice.php',
'className' => 'tx_rsmysherpasusers_authservice',
)
);

Still it would be a good idea to implement this option into the felogin extension and control it by typoscript setup - including 'auth service priority'.

Regards
Heiko Hänsge

oh, I somehow missed out the 1st comment. tested it and works great as ext. thanks also for mentioning the uniqueInPid issue, Jigal. I'd be fine if this issue is closed.