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Branching Webhook Sends Foreign Apikey Causing 401 On Cross-Project Edge Functions

When a branching webhook's notify-url targets an Edge Function on a different Supabase project, the webhook sender injects the source project's publishable key into the apikey header. The target project's API gateway rejects the request with 401 UNAUTHORIZED_INVALID_API_KEY before the function executes, breaking cross-project DevOps workflows.

highConfidence 85%Supabase

Origin Analysis

The webhook dispatcher always includes the source project's publishable API key in the apikey header, regardless of the target host. When the notify URL points to another Supabase project, that target gateway authenticates the key against its own project, fails validation, and returns 401 before the Edge Function runtime can process the request.

1. Create two Supabase projects: MAIN (product) and DEVOPS. 2. Deploy an Edge Function on DEVOPS, e.g. notify-slack. 3. On MAIN, configure the branching webhook with: supabase branches update main --notify-url https://<DEVOPS_PROJECT_REF>.supabase.co/functions/v1/notify-slack 4. Trigger a branching event (push or merge). 5. Observe that the DEVOPS Edge Function does not execute; logs show 401 UNAUTHORIZED_INVALID_API_KEY and the injected apikey header has prefix sb_publishable_$MAIN_PROJECT_PUBLISHABLE_KEY.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

This change may affect existing same-project webhooks if they rely on the apikey header being present; the logic preserves that behavior for matching hosts. However, if a user previously targeting another project relied on the source apikey (even though it caused 401), they may need to explicitly configure a custom header. Rolling back to the previous behavior is straightforward by reverting this change, but that would reintroduce the cross-project 401. Additionally, ensure that custom header injection does not allow overriding critical headers (e.g., a malicious notify-url could try to override Content-Type or other security headers); validate and sanitize customHeaders before merging.