Add OTP function

[PythonCoderAS]

Per praw-dev/praw#1496 this will allow OTPs (2fa codes) to be supplied hourly instead of being appended to the password.

[jarhill0]

This is surprisingly simple to implement. Can you also add tests and update the changelog?

Also, I'd like to hear @bboe's thoughts on this interface. I laid out the reasons why I like it in my comment.

[PythonCoderAS]

This is surprisingly simple to implement. Can you also add tests and update the changelog?

Also, I'd like to hear @bboe's thoughts on this interface. I laid out the reasons why I like it in my comment.

I can't currently test it because I don't have access to my 2FA authenticator device.

[bboe]

I too am really surprised at how easy adding this support turned out to be. That's awesome. I just have one comment on naming, otherwise, this is awesome!

[MaybeNetwork]

I think that this needs a corresponding change in PRAW to work, similar to the one in my first suggestion. Without one, when you try to authenticate, PRAW executes the following block

if self.config.username and self.config.password:
            script_authorizer = ScriptAuthorizer(
                authenticator, self.config.username, self.config.password
            )
            self._core = self._authorized_core = session(script_authorizer)

which doesn't use the otp_function.

[PythonCoderAS]

I think that this needs a corresponding change in PRAW to work, similar to the one in my first suggestion. Without one, when you try to authenticate, PRAW executes the following block

if self.config.username and self.config.password:
            script_authorizer = ScriptAuthorizer(
                authenticator, self.config.username, self.config.password
            )
            self._core = self._authorized_core = session(script_authorizer)

which doesn't use the otp_function.

I'm going to make a PR for that once this gets through first.

[MaybeNetwork]

I can write and run the tests for this, and then add the corresponding feature to PRAW. If it's possible, add me as contributor to this PR. Otherwise I can make a separate PR.

[LilSpazJoekp]

You'll have to open a PR.

I would cherry-pick the commits from this branch and then add your own commits after that.