Add support for SRP Login

[abiligiri]

• Switch to use https://github.com/adam-fowler/swift-srp with some modifications that are local
  • Pad g value to equal size of N while calculating clientProof
• Use SHA256(plain-text-password) while computing key using PBKDF2
• Added a unit test with some sample values

Fixes #630

[fiznool]

Personally, I like the approach of using a well-tested library for SRP, and the upstream library seems to provide this. So I would be in favour of this implementation vs #639

If I can make a suggestion, forking adam-fowler/swift-srp and publishing as a separate package with the necessary changes would be my preference for the following reasons:

• any changes to the upstream code can be more easily incorporated into a fork
• the shared package can be consumed by the Xcodes app and cli

[abiligiri]

Note that both options use a library for SRP. This uses https://github.com/adam-fowler/swift-srp/blob/main/Sources/SRP/client.swift and #639 fixes the srp code that was already in repo most likely from https://github.com/Bouke/SRP. I see that Adam Fowler implementation is still active. Maybe that is another reason to use it.

@MattKiazyk I was able to download and install Xcode 16.1.0. Not sure what you mean by download doesn't work.

[abiligiri]

May I also request merging this for the release #632

[abiligiri]

I cleaned this up a bit. Using patched swift-srp from https://github.com/abiligiri/swift-srp and removed local copy. I have also opened MR for upstream adam-fowler/swift-srp#13

[MattKiazyk]

@abiligiri hope you don't mind I clean up some extra prints that were in there as well as moved the swift-srp dependency to an xcodes fork. I copied your changes from your branch into main on our fork.