I was wondering if anybody knows a way to authenticate a user without asking for a password. I have searched but haven't found a thing. I'm not looking for facebook authentication or something like that.
Maybe you could help me.
yes, do a two factor authentication without the first factor. So when people register for your application, have them chose email, or sms, or both, as a verification method. Verify their identity by sending an email (or sms) with a code they have to enter.
Once you verify their ownership of the email/phone number, going forward, every time they want to login, they enter their email (or phone number) and click "send me code", you send them a one time code that expires in 5 minutes or upon login, they enter the code and login.
Next time they want to login, ditto. This way you are not storing/hashing/encrypting passwords that can be hacked/stolen. It is their responsibility to maintain security of their email/phone, not yours.