Change Details

See T375954#10185685 for details. Probably we want to: * add a new opt-in mecahanism that uses the UserName cookie and a new user preference * add a configuration variable for randomly opting in some % of users at signup / temp user creation (or maybe those should be two separate variables, given that temp user issues are harder to recover from)

Adapt {T384549} for signup. We can set the opt-in flag once the user account got created, to make subsequent login flows consistent with the signup flow, but for a signup we need to decide on the fly. Probably what we want is to adjust the `isSul3Enabled()` check in `SpecialPageBeforeExecuteHookHandler::onSpecialPageBeforeExecute()` (responsible for deciding which flow to use): if the user is not logged in, and isn't actively opted in or opted out, use a site configuration flag to determine with what probability the user ends up in SUL3. This should still be overridable (there will be an opt-out link per {T377140} leading to the old signup page, and so the `usesul3=0` flag needs to reliably work there). Probably easiest to do as a new `$wgCentralAuthEnableSul3` type that takes lower priority than most other options; but unlike the `always` option, it must be specific to signup. Or maybe we should just split `$wgCentralAuthEnableSul3` into a login and a signup version.

See T375954#10185685 for detailsAdapt {T384549} for signup. We can set the opt-in flag once the user account got created, to make subsequent login flows consistent with the signup flow, but for a signup we need to decide on the fly. Probably what we want is to adjust the `isSul3Enabled()` check in `SpecialPageBeforeExecuteHookHandler::onSpecialPageBeforeExecute()` (responsible for deciding which flow to use): if the user is not logged in, and isn't actively opted in or opted out, use a site configuration flag to determine with what probability the user ends up in SUL3. This should still be overridable (there will be an opt-out link per {T377140} leading to the old signup page, and so the `usesul3=0` flag needs to reliably work there). Probably we want to: * add a new opt-in mecahanism that uses the UserName cookie and a new user preference * add a configuration variable for randomly opting in some % of users at signup / temp user creation (or maybe those should be two separate variables,easiest to do as a new `$wgCentralAuthEnableSul3` type that takes lower priority than most other options; but unlike the `always` option, it must be specific to signup. given that temp user issues are harder to recover from)Or maybe we should just split `$wgCentralAuthEnableSul3` into a login and a signup version.