Add faster `/authorize/github` alternative
Add faster `/authorize/github` alternative

The `/authorize/github` needs to load and boot the whole Ember app before it can continue, which significantly slows down the login process. Since we don't need any of that for the `postMessage()` call we can instead use a regular HTML file with a short snippet of inline JavaScript to accomplish the same without having to load several kilobytes of JS.

rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io