implement WKD client class

[tomholub]

part of #1298

This issue is a subset of #1201 as follows:

1. port Wkd class from browser extension
2. add tests for it independently of the rest of the codebase, merge the class unused

I hope we can ideally find a WKD client implementation done in Java so we don't have to re-implement it. If there isn't any, I hope we can at least find z-base-32 hash algorithm so we don't have to implement this low level code. If there isn't even that, we'll have to implement these.

[IvanPizhenko]

@tomholub I could not find ready Java client library for WKD, but it looks like it should not be very hard to implement it.
Regarding ZBase32 - there is library (actually additional codec for the Apache Commons Codec framework)
https://mvnrepository.com/artifact/com.sandinh/zbase32-commons-codec
MIT or Apache 2.0 license (according to Maven Central, it indicates 2 different license on 2 pages):

• Indicates Apache 2.0 license here: https://mvnrepository.com/artifact/com.sandinh/zbase32-commons-codec_2.12/1.0.0
• and MIT License here: https://mvnrepository.com/artifact/com.sandinh/zbase32-commons-codec_2.12

No explicit license in source code on Github (https://github.com/ohze/zbase32-commons-codec).

Asked author to add license: ohze/zbase32-commons-codec#1

[IvanPizhenko]

Btw, zbase32 is not hash algorithm, it is data encoding algorithm, like base64.
Some more info from the Internet:
It uses human-centered alphabet of 32 characters. The most elaborate symbol table to facilitate writing, pronunciation and memorization of coded information. The authors have rearranged the most human-friendly symbols to the positions that are used most often. Encoding table is ybndrfg8ejkmcpqxot1uwisza345h769. Also, there are no special characters at the end of the encoding result.

[IvanPizhenko]

@tomholub So I still not sure should we use that zbase32 library or not because it is uncertain which license does it use. Please check it and explicitly approve or deny.

[tomholub]

Thank you for checking this thoroughly! 👍

Both Apache 2.0 and MIT License, or a combination, is fine. Let's start using it, and if it turns out the license is something else, we'll have to re-implement it.

Sorry for the brain fart in the description, of course it's an encoding mechanism, a pretty simple one.

[tomholub]

Here is the actual class to port - sorry I failed to mention it earlier:

https://github.com/FlowCrypt/flowcrypt-browser/blob/master/extension/js/common/api/key-server/wkd.ts

[tomholub]

I now see I mentioned it, just forgot to link it.

[IvanPizhenko]

Thank you!