Add support for keyboard-interactie auth.

[mateuszkj]

What

This change adds support for the keyboard-interactive authentication method described in RFC 4256.

Implementation

This solution introduces the AuthKeyboardInteractive builder, which can be converted into an AuthMethod.

let kbi = AuthKeyboardInteractive::new()
    .with_response("Password: ", "abt")
    .with_response("OTP: ", "12345");

let auth = AuthMethod::with_keyboard_interactive(kbi);
...

This implementation allows defining responses to known and exact prompts.

Implementation Considerations

Although my solution addresses my problem, it might be too limited for others. Here are some considerations:

• Should prompts be trimmed of white spaces before comparison?
• Should prompt comparisons be case-insensitive?
• Should we add an async handler so API users can implement custom responses (e.g., asking SMS services for OTPs)?

If the answer to any of these questions is yes, I am willing to implement those changes.

[Miyoshi-Ryota]

@mateuszkj
Sorry for the late response. I'm caught up in a death march at my main job and couldn't find time.

Thanks for the excellent changes. LGTM!

I'll go ahead and merge it.

I'll just fix some minor lint warnings in the CI and then release it. I'll release your contributions to crates.io this weekend.

Implementation Considerations

I'm a bit interested in the third point, but we can address it when the need arises. I prioritize releasing what's needed now over waiting for a perfect solution.

Thank you for your perfect pull request!

[mateuszkj]

@Miyoshi-Ryota Thanks for merging it.

If you need help with any implementation, feel free to contact me. I'm also considering adding SSH-agent support, so there might be a need for an async credential provider then.