grafana: disable PKCE for the generic_oauth flow#600
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Grafana is a confidential client authenticated with CLIENT_SECRET_BASIC. PKCE is designed for public clients that cannot protect a client secret; for confidential clients the client secret already authenticates the token exchange and PKCE adds no meaningful security. With use_pkce=true, Grafana generates a code_verifier, stores it in a browser session cookie alongside the OAuth state, then sends it in the token request. If that cookie is absent or invalid (different tab, browser restart, Safari ITP expiry, proxy stripping Set-Cookie), Grafana omits the verifier from the token request. Spring Authorization Server stored the code_challenge at the authorize step, so it now sees a stored challenge with no matching verifier and rejects the exchange — surfacing as "Failed to get token from provider" on the login page. Setting use_pkce=false removes the browser-state dependency and leaves the auth-api client registration unchanged (requirePkce=false). The flow is: authorize → cookie-free state param → code → secret-authenticated token exchange.
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Grafana is a confidential OAuth2 client authenticated with
CLIENT_SECRET_BASIC. PKCE is designed for public clients that cannot protect a secret; for confidential clients the client secret already authenticates the token exchange.With
use_pkce: true, Grafana generates acode_verifier, stores it in a browser session cookie alongside the OAuthstate, and sends it in the token request. If that cookie is missing or invalid (different browser tab, browser restart, Safari ITP expiry, a proxy strippingSet-Cookie), Grafana omits the verifier from the token POST. Spring Authorization Server stored thecode_challengeat the authorize step, so it sees a stored challenge with no matching verifier and rejects the request — surfacing as "Failed to get token from provider" on the Grafana login page.use_pkce: falseremoves the browser-state dependency entirely. The auth-api client registration remainsrequirePkce: false, so the flow is: authorize → code (with state, no PKCE) →CLIENT_SECRET_BASIC-authenticated token exchange.After merge: a Grafana pod restart is required (
kubectl -n observability rollout restart deploy grafana) for the new config to take effect. If Grafana login still fails after the restart, also verify that the Vault secrets atsecret/auth-api(auth.clients.grafana.secret) andsecret/platform/observability(grafana.oauth_client_secret) are identical — re-runningtmp.sh'spaircall and restarting both auth-api and Grafana will re-align them.