Help using api with Vala?

Simply put, I want to make a vala app for danbooru browsing but ran into a hitch authenticating using json.

I ended up stripping up everything down to just seeing if I can get a proper answer to no avail-- I am doing something painfully wrong and it escapes me, and any help would be appreciated with getting past this hurdle.

The repo of what I have is here: https://github.com/Midiman/Makoto

Basically, i am doing something stupid and I don't know where. Mind helping :^)?

Compare:

var uri = "http://danbooru.donmai.us/post/index.json?limit=1?login=%s?password_hash=%s".printf(username, hash.compute_for_string(ChecksumType.SHA1, combined_string, -1));

var uri = "http://danbooru.donmai.us/post/index.json?limit=1&login=%s&password_hash=%s".printf(username, hash.compute_for_string(ChecksumType.SHA1, combined_string, -1));

Welp, that would have been something to check the first time.

Thank you for that.