litellm already supports Google, Microsoft and generic OIDC SSO through
fastapi-sso, which has no SAML support; AuthMethod.SAML existed only as an
unused enum value. This adds real SAML 2.0 single sign-on for the admin UI.
A new SAMLAuthHandler validates signed assertions with the OneLogin
python3-saml toolkit and maps them onto a CustomOpenID, then reuses the
shared post-login path every other provider goes through, so provisioning,
role/team mapping and the UI session JWT are unchanged. Both SP-initiated
and IdP-initiated HTTP-POST flows are supported. SP-initiated logins are
bound to the browser that started them via an HttpOnly state cookie plus a
cached AuthnRequest id, and the ACS rejects any response whose InResponseTo
doesn't match; unsolicited (IdP-initiated) responses cannot be browser-bound
so they are rejected unless SAML_ALLOW_UNSOLICITED=true. Replays are rejected
by a consumed-assertion guard whose lifetime tracks each assertion's
NotOnOrAfter, and both the replay guard and the login-state binding go
through the proxy's shared in-memory + Redis cache for multi-instance
deployments. The ACS honors DISABLE_ADMIN_UI and re-applies the
free-SSO-user Enterprise gate after the assertion is validated, so an
unvalidated POST can no longer drive the billable-user count query.
SAML is configurable from the admin UI SSO settings (IdP metadata URL or
inline XML, SP entity ID, and an allow-unsolicited toggle), which persists
the SAML_* environment variables the handler reads, exactly like the Google,
Microsoft and generic OIDC providers.
python3-saml is kept as an optional saml extra; its xmlsec and lxml wheels
bundle the native libraries so no system packages are required, and the
import is guarded so the proxy still starts without the package with the
SAML routes returning a clear 501.
Resolves LIT-4016
The SSO and Email Server settings pages read only stored config, so a gateway
configured entirely through environment variables rendered every field blank
even though both features were live. Rather than add per-endpoint env fallback,
resolve each setting through one typed config object.
A FieldDescriptor names, for one setting, where it lives in the stored row
(db_key), which process env var carries it (env_var), whether it is a secret,
and its effective default. A pure resolve_fields reconciles a descriptor table
against the stored row and the process environment with a fixed precedence and
reports per-field provenance (db, env, default, or unset). The SSO descriptor
table single-sources the field-to-env mapping that the read and write paths
previously duplicated, so they can no longer drift.
get_sso_settings and the /get/config/callbacks alerting block read through the
resolver instead of their own inline fallbacks. get_sso_settings no longer
decrypts stored values into os.environ; decryption happens once inside the
resolver via the pure helper, so a GET stops mutating the process environment.
The SSO response carries provenance so the UI can distinguish an env-sourced
value from a stored one, and secrets are masked at the endpoint (the resolver
returns them unmasked so the login path could consume them). os.environ remains
the runtime carrier; the SSO login and mail-send paths are unchanged.
The settings pages also submit only fields an admin actually edited, so a
rendered mask or env-sourced value is never written back over a working
secret, and generic_scope is a real SSO form field. Omitting a field from
/update/sso_settings clears it, which provider switching relies on; the deeper
write-path concern that behaviour points at is tracked in LIT-4498.
