Add getUserPasswordHash() and auth using hash

[Sn4k3r]

Add getUserPasswordHash() which returns base64 hash.
Now you can use Username&Password or stored base64 hash for
authentication

[earlephilhower]

Thanks for your PR, but the core and libraries have changed enough that this PR now has a merge conflict.

Could you merge it manually with the latest core, so we can consider it for future releases?

[earlephilhower]

After reviewing this, I don't see any use case. Since the hash itself is just the b64 encoding of the raw user/pass, it's no more secure than putting them in plaintext in the app.

Seeing as it's also ancient, abandoned, and has merge-conflicts I'm closing.