OpenCode MCP Auth in GitHub Codespaces redirects to a non-existent page

[affan2021shaikh]

Bug report

• I confirm this is a bug with Supabase, not with my own application.
• I confirm I have searched the Docs and GitHub Discussions.
• I confirm I have searched the Discord.

Describe the bug

When authenticating Supabase MCP in OpenCode, after clicking Authorize OpenCode, it redirects to http://127.0.0.1:19876/mcp/oauth/callback&state=**************************************************************** which has no response data at all. This happens in GitHub Codespaces.

To Reproduce

Steps to reproduce the behaviour:

1. Go to 'https://github.com/codespaces'
2. Click on '`New codespace'
3. Pick any options
4. Run the following in the terminal:

npm i -g opencode-ai
cat > .opencode/opencode.json <<'EOF'
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "supabase": {
      "type": "remote",
      "url": "https://mcp.supabase.com/mcp?project_ref=tiokvmuyfgcnagnelpib&features=docs%2Caccount%2Cdatabase%2Cdebugging%2Cdevelopment%2Cfunctions%2Cbranching%2Cstorage",
      "enabled": true
    }
  }
}
EOF
opencode mcp auth supabase

5. Wait and when it appears, ⌘-click on the link.
6. Click Authorize OpenCode.

Expected behavior

Closure of tab and authentication confirmation in terminal.

Screenshots

If applicable, add screenshots to help explain your problem.

System information

• OS: macOS Tahoe 26.5.2 (25F84)
• Browser: Firefox Nightly (155.0a1 (2026-07-21) (aarch64))
• Version of Node.js: v24.14.0

Additional context

Same problem has happened before with Gemini CLI

[ElectricCodeGuy]

Yep. Only happens sometime... Super annoying. If you keep one retying it suddenly works

[jumski]

Thanks for the report @affan2021shaikh ! Yeah, this one's on opencode - the OAuth callback listens on 127.0.0.1, but in browser-based Codespaces that points to your laptop, not the Codespace, so the callback never gets there. Needs a fix on the opencode side; I'm on it and will post here when it lands.

@ElectricCodeGuy interesting that retrying sometimes works for you. Are you using Codespaces in the browser or VS Code Desktop? When it works, does the callback still open 127.0.0.1:19876, or a *.app.github.dev URL? And are you retrying in the browser or rerunning opencode mcp auth?