iOS 11 Safari: How to pass user/password in URL for Basic Authentication?
According to the RFC at https://tools.ietf.org/html/rfc3986#section-3.2.1 this feature is deprecated, so I'm pretty sure it is disabled on purpose.

Chrome also does this: https://bugs.chromium.org/p/chromium/issues/detail?id=504300

Remembering users is what cookies are for, not using them severely limits your options. I guess you could write a login token service that generates URL's like https://yoursite.com/login/236cq827hr6xqoxxrm9q9r which logs in the user immediately. I would make sure it did not work over regular HTTP first, though.