NFC support

[xxv]

Possibly related to #4, add support for NFC tags. Ideally, this should allow for one of:

• Using the NFC tag ID as [part of] the "salt". This adds a little protection over not using them at all, as it adds semi-private information to the mix when the information is otherwise globally public. This should probably be in the form of either "XXXXXX" or "XX:XX:XX", where XX is a byte of the NFC tag ID.
• Store an NDEF record with an arbitrary sized amount of randomly-generated data. The same data should be readable by the app and exportable, encoded in base64. Maybe have a slider for number of bytes based on total tag storage?
• Use whatever data is already on a tag as a "salt". Not sure if this is a good idea.

There needs to be a clear visualization of the contents of a given tag when it is scanned, while ideally not exposing the tag contents itself. The password visual hash could be used for this, but should have a small variation to it to make its context clear (password vs. "salt") (undecided about this part). This should be presented near the password entry form, ideally visually indicating that it's suffixed to the master password.

In doing some research on the ability to add a custom drawable span to a password form (think ••••••[NFC #1282374]), it's not possible to do as all spans are stripped from an EditText widget when it's in password mode.

[xxv]

After plenty of investigation, Spans that do this are doable, but there's at least one bug in Android that prevent it from being something easy to add. So instead, for now, this should just append the contents of the tag to the master password field.

[xxv]

Closed by de08422a40626f2e960455cfffb3edace4b30151 .