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fix(mcp): pin fastmcp<4.1.7 to restore hosted SSO login - #1465
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Aaron ("AJ") Steers (aaronsteers) merged 4 commits intoNov 12, 2026
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… login Co-Authored-By: AJ Steers <aj@airbyte.io>
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I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".
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Code coverage overviewLanguages: Python Python / code-coverage/pytest-no-creds
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…ay unique Co-Authored-By: AJ Steers <aj@airbyte.io>
Co-Authored-By: AJ Steers <aj@airbyte.io>
…ires unique source IDs Co-Authored-By: AJ Steers <aj@airbyte.io>
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changed the title
_set_consent_binding_cookie signature
Aaron ("AJ") Steers (aaronsteers)
marked this pull request as ready for review
November 12, 2026 15:21
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Devin Review🟢 Devin Review found nothing to fix · View findings |
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fastmcp<4.1.7 to restore hosted SSO login
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🟢 Approval recommended
No active review issues are reported for the FastMCP compatibility update.
No open issues 🎉
What changed in this PR
This PR addresses hosted Cloud MCP login failures caused by incompatible FastMCP consent-cookie APIs. It narrows the dependency range and strengthens startup compatibility checks for the custom SSO proxy.
Changes:
- Constrains FastMCP to
>=4.0.9,<4.1.7and locks it to4.1.6. - Checks parameter names for both consent-binding methods so incompatible signatures fail at startup.
- Adds a signature-change regression test and names the fake MultiAuth verifier to avoid duplicate provider IDs.
| File | Description |
|---|---|
uv.lock |
Locks FastMCP to 4.1.6 and refreshes affected transitive dependencies. |
tests/unit_tests/test_mcp_sso_auth.py |
Tests rejection of an incompatible consent-cookie method signature. |
tests/unit_tests/test_mcp_http_main.py |
Assigns the fake verifier a distinct MultiAuth identifier. |
pyproject.toml |
Caps FastMCP below the incompatible 4.1.7 release. |
airbyte/mcp/_sso_auth.py |
Adds consent-binding signature checks and updates compatibility documentation and errors. |
Review effort: Balanced
Aaron ("AJ") Steers (aaronsteers)
enabled auto-merge
November 12, 2026 15:28
Aaron ("AJ") Steers (aaronsteers)
merged commit Nov 12, 2026
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Aaron ("AJ") Steers (aaronsteers)
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devin/1794492938-fix-sso-consent-cookie-fastmcp
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November 12, 2026 15:31
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Overview
👉 TL;DR: Fixes the hosted Cloud MCP login, which has been failing with a server error for every user since 2026-11-06. It pins the auth library back to a stable release so the hosted image can no longer pull in an alpha build, and makes the server refuse to start if that library's internals ever change shape again.
Specifically, this pins
fastmcp>=4.0.9,<4.1.7and extendscheck_fastmcp_compatibility()to check the signatures of the privateOIDCProxyconsent-cookie methods thatAirbyteSsoOidcProxycalls.Changes
pyproject.toml:fastmcp>=4.0.9,<5.0→fastmcp>=4.0.9,<4.1.7.uv.lockmovesfastmcp/fastmcp-slimfrom 4.0.9 to 4.1.6.airbyte/mcp/_sso_auth.py: the new_CALLED_FASTMCP_METHOD_PARAMSgives the expected parameter names of_set_consent_binding_cookieand_verify_consent_binding_cookie.check_fastmcp_compatibility()now fails at startup when either one doesn't match. The existing_set_consent_binding_cookie(request, response, txn_id, token)call is unchanged.tests/unit_tests/test_mcp_sso_auth.py: a new test confirms that the check names a changed_set_consent_binding_cookiesignature.tests/unit_tests/test_mcp_http_main.py: theMultiAuthtest now names its fake verifier (verifiers={"headless": verifier}). fastmcp 4.1.6 rejects duplicate source IDs, and its two identical fakes collided.Review Spotlight
Reviewers with limited time, please review first:
pyproject.toml#L48: the pin_sso_auth.py#L704-L740: the startup signature checkRoot cause
uv pip install --prerelease=allow, so PyAirbyte'suv.lockis not used.fastmcp>=4.0.9,<5.0resolved to4.2.0a3for1.0.0-rc.42, and it resolves to4.2.0a4today.4.1.7+, droppedrequestfrom the private_set_consent_binding_cookie. EveryPOST /auth/login(Airbyte Cloud and SSO) then raisesTypeError: ConsentMixin._set_consent_binding_cookie() takes 4 positional arguments but 5 were given.<4.1.7excludes4.1.7pre-releases and every4.2.0a*, even with--prerelease=allow.Risks
fastmcp4.1.7+ alongside this release until the pin is lifted. Lifting it means changing the call to the new signature, and the startup check will flag that.AIRBYTE_MCP_SSO_OIDC_CONFIG_URL_TEMPLATE, so they never serve the SSO login page.Follow-ups
Test plan
uv run pytest tests/unit_tests/test_mcp_sso_auth.py tests/unit_tests/test_mcp_http_main.py: 143 passed.ruff checkandruff formatpass./authorize→/auth/login→POST /auth/login) against a localhttp_mainwith SSO login enabled and pointed atcloud.airbyte.com. Both builds were installed the way the image does it (--prerelease=allow):airbyte==1.0.0rc42(fastmcp4.2.0a4) returns 500 with theTypeErrorabove. This matches what prodmcp.airbyte.comreturns today.4.1.6) returns 302 to the Keycloak authorize URL.Link to Devin session: https://app.devin.ai/sessions/372eb3109e3742879489bff8d6b26bb0
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