Not downplaying the possibility of a problem on Azure's end, but the most likely scenario is your credentials have leaked, possibly (as another commenter suggests) though a stack overflow post, GitHub issue, or similar. If someone has a valid key and queue name they can post to it. That's the most likely cause.
LLMs tokens are usually common word or parts of word, and it would be extremely weird for copilot to output them verbatim in generated code(I've actually tried a few times), or it would be random invalid keys since there is no real patterns in API keys
+I'd be shocked if they weren't automatically stripped from the training data
I’m sure there are edge cases, but I’ve been surprised how well it handles this.
The repo is somewhat niche, and copilot will nearly (with some help) create the entire repo, including the original repos comments.... but won't generate the same keys no matter how hard I've tried.
I'm pretty sure there was some at least some sanitization before it made its way into the model.