feat(auth): support separate OIDC discovery URL for back-channel calls#369
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Add an optional oidc_discovery_url (NEBI_AUTH_OIDC_DISCOVERY_URL) that decouples where nebi fetches .well-known/openid-configuration from the issuer it validates in the token's "iss" claim. In split-horizon deployments the public issuer URL that browsers use may not be resolvable from inside the cluster, so OIDC initialization fails on the discovery fetch and never recovers. When oidc_discovery_url is set, discovery is fetched from it (e.g. an in-cluster Keycloak Service) while "iss" is still validated against oidc_issuer_url, using oidc.InsecureIssuerURLContext to tell go-oidc the two are intentionally different. When unset, behavior is unchanged: discovery and issuer validation both use oidc_issuer_url.
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aktech
approved these changes
Jun 4, 2026
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Closes #371
What
Adds an optional
oidc_discovery_url(NEBI_AUTH_OIDC_DISCOVERY_URL) that decouples where nebi fetches.well-known/openid-configurationfrom the issuer it validates in the token'sissclaim.Why
In split-horizon deployments the public issuer URL that browsers use is not resolvable from inside the cluster. Today nebi uses a single
oidc_issuer_urlfor both discovery andissvalidation, so OIDC init fails on the discovery fetch and loops forever:This came up deploying the nebari-nebi-pack into a private cluster where Keycloak sits behind an external gateway (browsers can reach it, in-cluster pods can't). See nebari-dev/nebari-nebi-pack#13.
How
When
oidc_discovery_urlis set, discovery is fetched from it (e.g. an in-cluster KeycloakService) whileissis still validated againstoidc_issuer_url, usingoidc.InsecureIssuerURLContextto tell go-oidc the two are intentionally different. When unset, behavior is unchanged — discovery and issuer validation both useoidc_issuer_url.Operator note
This is the same issuer-vs-discovery split that nebari-dev/nebari-operator#112 is tracking for the gateway's
SecurityPolicy.oidc. This PR covers nebi's own direct OIDC (used by the CLI device-code flow); the two should stay consistent.Deployment caveat (not a code concern)
Discovery is necessary but not sufficient. After discovery, the endpoints in the document (
token_endpoint,jwks_uri) are what nebi calls for code exchange and token verification. The IdP must return in-cluster-reachable URLs for those — for Keycloak that meanshostname-backchannel-dynamic=true(KC_HOSTNAME_STRICT_BACKCHANNEL=false) so that fetching discovery via the internal URL echoes internal back-channel URLs. nebi leaves the endpoints as the IdP returns them.Tests
internal/auth/oidc_test.go:DiscoveryURLwith a mismatched (public) issuer succeedsDiscoveryURL) still rejects anissthat doesn't match the discovery URLgo test ./internal/auth/...,go vet, andgofmtall clean.Related Issues