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Max Peintner
d488ecb07f
# Which Problems Are Solved When an OIDC authorize request carries a `login_hint` that resolves via domain discovery to an organization configured to auto-redirect to a single external IdP, Login V2's server-side flow initiation returns a malformed `Location` header: the login base path is concatenated with the absolute IdP authorize URL without a separator (e.g. `https://<instance>/ui/v2/loginhttps://login.microsoftonline.com/...`). The flow ends in `{"code":5,"message":"Not Found"}` and the IdP is never contacted. The same IdP works when the user submits the login name interactively, because the client-side handler distinguishes external URLs; only the server-side `login_hint` fast-path introduced in #12431 is affected. Additionally, the same fast-path only handled the `redirect` response shape from `sendLoginname`. When the discovered organization's IdP is SAML with POST binding, `sendLoginname` returns `samlData` (form fields instead of a URL), which was silently ignored — the user fell back to the prefilled `/loginname` screen instead of being signed in silently, unlike the client-side flow, which auto-submits the SAML AuthnRequest form. # How the Problems Are Solved `resolveLoginHint` passed every redirect returned by `sendLoginname` through `constructUrl`, which unconditionally prepends `NEXT_PUBLIC_BASE_PATH` and assumes a relative path. It now checks `isExternalUrl` first: absolute URLs are validated with `isSafeRedirectUri` (blocking `javascript:`/`data:`/etc., falling back to `/loginname` if unsafe) and redirected as-is, while relative paths keep being resolved against the base path — matching the handling already used in the idp-scope branch of `handleOIDCFlowInitiation` and in the client-side `handleServerActionResponse`. `resolveLoginHint` also handles the `samlData` response shape now: after validating the target URL with `isSafeRedirectUri`, it responds with the same auto-submit HTML form used by the existing SAML flows, so a `login_hint` resolving to a POST-binding SAML IdP completes silently as well. Since this form was previously duplicated inline three times in `flow-initiation.ts`, it is extracted into a shared `buildAutoSubmitFormResponse` helper used by all call sites. Regression tests cover the absolute-URL redirect (fails on the previous code with the exact malformed URL), the SAML POST auto-submit response, and the unsafe-scheme fallbacks for both shapes.