5 posts tagged with "troubleshooting"

A Keycloak infinite redirect loop at login almost always means one thing: a cookie Keycloak set on the way to the login page did not come back on the way out of it. Keycloak has no session to resume, so it starts the flow again, and the browser bounces between your application and /protocol/openid-connect/auth until it gives up.

The reason this is so common is in the Set-Cookie headers. Keycloak 26.8.0 marks every cookie in the login flow Secure; SameSite=None, unconditionally — there is no setting that relaxes it. A browser will not store a Secure cookie that arrives over plain http://, and it will not store SameSite=None without Secure. So the loop is usually not an OIDC problem at all. It is a transport problem that the OIDC layer reports as a lost session.

A Keycloak 403 Forbidden always means the same thing: your token was accepted, and the permissions attached to it were not enough. That is the whole difference from a 401, which means the token itself was rejected — missing, expired, malformed, or signed by another realm. Checking which of the two you have is the fastest useful thing you can do, because 401 sends you to the token and 403 sends you to role mappings, and they share no fixes.

After that, the question is which surface returned it. The Keycloak admin console, the Admin REST API and your own application all return 403 for unrelated reasons, and the response body tells you which one you are looking at without any further digging.

A Keycloak CORS error is almost never a CORS-configuration problem in the general sense. There is no CORS server setting to turn on. Keycloak decides per request by comparing the browser's Origin header against the Web Origins list on the OIDC client named in that request, using exact string matching. If it matches, the response carries Access-Control-Allow-Origin. If it does not, you get 403 with the body {"error":"Invalid origin"} — and the browser reports it as a CORS failure, which sends most people to the wrong place.

So the first thing to do is not to read a CORS guide. It is to open the Network tab, find the failing request, and check whether the status is 403 with that body. That single fact splits every cause below into two halves.

Keycloak returns invalid_grant for at least eight unrelated failures, and the error code itself tells you nothing. The useful field is error_description, which Keycloak fills in with a short string that maps almost one-to-one onto a cause:

{"error":"invalid_grant","error_description":"Code not valid"}

invalid_grant is OAuth's designated bucket for "the grant you presented is no good", so Keycloak uses it for expired codes, replayed codes, PKCE mismatches, rotated refresh tokens, dead sessions, revoked offline tokens, and bad passwords alike. Read the description, find it in the table below, stop guessing.

Everything here was run against Keycloak 26.7.3 on 2026-09-07, with realm defaults except where a test says otherwise.

You clicked "Log in", Keycloak showed you "We are sorry… Invalid parameter: redirect_uri", and no amount of staring at the admin console explains why.

The short answer: the redirect_uri your application sent does not match, character for character after wildcard expansion, any entry in that client's Valid redirect URIs. The long answer is that Keycloak's matching rules are stricter and stranger than almost everyone assumes — in particular, it will reject any redirect_uri containing a query string, no matter what you registered.

Everything below was tested against Keycloak 26.7.3.