VS Code forks: "Missing required parameter: redirect_uri" on auth

[hendrikgaffo]

Describe the bug
I wanted to give Trae a shot, since I've heard positive things about it multiple times.

Obviously, I wanted to use the Mermaid-Chart extension with it. Trae, like many VS Code forks, uses open-vsx to provide extensions and this is the Mermaid-Chart extension available.

The installation is seamless, however, when trying to login, the error Missing required parameter: redirect_uri is displayed. This is not true, though. A valid (in the sense of syntactically correct) redirect_url is passed as param to the auth URL.

My uneducated guess is that, since Trae uses the trae:// System Handler, somewhere in your code you expect the official VS Code System Handler string and in case it's missing, you assume that the entire redirect_url is faulty.

To Reproduce
Steps to reproduce the behavior:

1. Go to trae.ai, download and install Trae (I think other forks like VS Codium or Cursor might work as well?)
2. Search for the vscode-mermaid-chart extension and install it
3. Try to authenticate with MermaidChart
4. See the HTTP 400 error with the message Missing required parameter: redirect_uri

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots

Desktop:

• OS: macOS 15.3.1
• Browser: Tested on Chrome and Edge (both with the most recent version available)

Additional context
See System Handler hypothesis above.