Currently I am using email and password to authenticate because that is how it came default when I created the project via the CLI. Also Adobe uses the same method to authenticate. The one problem with this is what if someone forgets what email they used for the account? How do you handle this situation in your application?

The application doesn't handle that. The user has to contact customer support to resolve it because it requires too much personal information to resolve in a secure way.

So the try every email address and we'll let you know if an account exists way is really bad?

The way I do it is by the "forgot password" link/button, even if they forgot what email they used. The I show them a field to enter the email address associated to the account, which is the one they can't remember. So after they enter the email address and submit the form, a messages states that "if the email address exists in the database, they will receive an email with instructions". This way they can test as many email addresses they want, just the one associated with a current account will actually trigger the action to send them the email. I hope it helps

That is actually how I am doing it now. I ask for the email and only send a password reset link if an account is found. I don't actually tell them if an account is found in the form itself though for security reasons.

If you (the company using the software you code) has the resources - I prefer the call Support version. Saying that - we do have in our software the ability to reset a password via Email. They are prompted to enter the email address for their account and get a message on submission that if it exists we'll send an email... blah blah... - like @Dani Szwarc, above.