diff --git a/backend/src/app/auth/oidc.clj b/backend/src/app/auth/oidc.clj
index 286ff3be45..4f7583d39d 100644
--- a/backend/src/app/auth/oidc.clj
+++ b/backend/src/app/auth/oidc.clj
@@ -761,6 +761,16 @@
 ;; ORG SSO HELPERS
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+(defn- non-blank-uri
+  [value]
+  (when-not (str/blank? value) value))
+
+(defn org-sso-discovery-uri
+  "Return the OIDC discovery URI from an org SSO config, preferring :issuer."
+  [sso]
+  (or (non-blank-uri (:issuer sso))
+      (non-blank-uri (:base-url sso))))
+
 (defn prepare-org-sso-provider
   "Build an OIDC provider map dynamically from the Nitrate org SSO config.
   Uses OIDC discovery via :base-url (or :issuer as fallback) when
@@ -770,12 +780,96 @@
                          {:type             "oidc"
                           :client-id        client-id
                           :client-secret    client-secret
-                          :base-uri         (some-> (or base-url issuer)
+                          :base-uri         (some-> (or (non-blank-uri base-url)
+                                                        (non-blank-uri issuer))
                                                     (str/rtrim "/")
                                                     (str "/"))
                           :scopes           (into default-oidc-scopes (or scopes #{}))
                           :skip-ssrf-check? true}))
 
+(defn build-org-sso-auth-redirect-uri
+  "Build the OIDC authorization redirect URI for an organization SSO config.
+  Raises if the config is incomplete or OIDC discovery fails."
+  [cfg sso & {:keys [dest-url organization-id provider]}]
+  (let [organization-id (or organization-id (:organization-id sso))
+        issuer          (org-sso-discovery-uri sso)
+        dest-url        (or dest-url (str (cf/get :public-uri)))]
+    (when-not issuer
+      (ex/raise :type :validation
+                :code :invalid-sso-config
+                :hint "missing issuer or base-url"))
+    (let [oidc-provider (or provider (prepare-org-sso-provider cfg sso))
+          state-token   (tokens/generate cfg {:iss             "oidc"
+                                              :dest-url        dest-url
+                                              :organization-id organization-id
+                                              :issuer          issuer
+                                              :exp             (ct/in-future "4h")})]
+      (build-auth-redirect-uri oidc-provider state-token))))
+
+(def ^:private probe-auth-code "penpot-sso-config-probe")
+
+(defn- decode-token-error-response
+  [body]
+  (when (and (string? body) (pos? (count body)))
+    (try
+      (json/decode body)
+      (catch Throwable _ nil))))
+
+(defn- token-endpoint-error
+  [response]
+  (some-> response :body decode-token-error-response :error d/name))
+
+(defn- token-endpoint-error-description
+  [response]
+  (some-> response :body decode-token-error-response :error-description))
+
+(defn- token-endpoint-valid-client-error?
+  "Token endpoint rejected the dummy auth code but accepted the client credentials."
+  [response]
+  (= "invalid_grant" (token-endpoint-error response)))
+
+(defn- token-endpoint-invalid-client-error?
+  "Token endpoint rejected the client credentials."
+  [{:keys [status] :as response}]
+  (let [error (token-endpoint-error response)
+        description (str/lower (or (token-endpoint-error-description response) ""))]
+    (or (= status 401)
+        (#{"invalid_client" "unauthorized_client"} error)
+        (and (= error "access_denied")
+             (str/includes? description "unauthorized")))))
+
+(defn- probe-org-sso-client-credentials
+  "Probe the token endpoint with a dummy authorization code.
+  Valid client credentials are expected to answer with `invalid_grant`."
+  [cfg provider]
+  (let [params {:client_id     (:client-id provider)
+                :client_secret (:client-secret provider)
+                :code          probe-auth-code
+                :grant_type    "authorization_code"
+                :redirect_uri  (build-redirect-uri)}
+        req    {:method  :post
+                :headers {"content-type" "application/x-www-form-urlencoded"
+                          "accept"       "application/json"}
+                :uri     (:token-uri provider)
+                :body    (u/map->query-string params)}
+        response (http/req cfg req {:skip-ssrf-check? (:skip-ssrf-check? provider)})]
+    (cond
+      (token-endpoint-valid-client-error? response) true
+      (token-endpoint-invalid-client-error? response) false
+      :else false)))
+
+(defn is-organization-sso-config-valid?
+  "Return true when the SSO config can be discovered, can build a login URL,
+  and the client credentials are accepted by the token endpoint."
+  [cfg sso]
+  (try
+    (if (org-sso-discovery-uri sso)
+      (let [provider (prepare-org-sso-provider cfg sso)]
+        (and (build-org-sso-auth-redirect-uri cfg sso :provider provider)
+             (probe-org-sso-client-credentials cfg provider)))
+      false)
+    (catch Throwable _ false)))
+
 (defn- auth-handler
   [cfg {:keys [params] :as request}]
   (let [provider (resolve-provider cfg params)
diff --git a/backend/src/app/loggers/audit.clj b/backend/src/app/loggers/audit.clj
index 9de442a48a..c1b63c9aff 100644
--- a/backend/src/app/loggers/audit.clj
+++ b/backend/src/app/loggers/audit.clj
@@ -88,7 +88,8 @@
   #{:session-id
     :password
     :old-password
-    :token})
+    :token
+    :client-secret})
 
 (defn extract-utm-params
   "Extracts additional data from params and namespace them under
diff --git a/backend/src/app/nitrate.clj b/backend/src/app/nitrate.clj
index c99451d6df..1f54c47121 100644
--- a/backend/src/app/nitrate.clj
+++ b/backend/src/app/nitrate.clj
@@ -14,7 +14,8 @@
    [app.common.schema :as sm]
    [app.common.schema.generators :as sg]
    [app.common.time :as ct]
-   [app.common.types.organization :as cto]
+   [app.common.types.organization :as cto
+    :refer [schema:nitrate-sso]]
    [app.common.uri :as u]
    [app.config :as cf]
    [app.http.client :as http]
@@ -430,17 +431,6 @@
                        [:permissions [:map-of :keyword :string]]]
                       params))
 
-(def ^:private schema:nitrate-sso
-  [:map
-   [:organization-id ::sm/uuid]
-   [:active [:maybe :boolean]]
-   [:provider [:maybe :string]]
-   [:client-id [:maybe :string]]
-   [:base-url [:maybe :string]]
-   [:client-secret [:maybe :string]]
-   [:issuer [:maybe :string]]
-   [:scopes [:maybe [::sm/set ::sm/text]]]])
-
 (defn- get-org-sso-api
   "Fetches the SSO configuration for an organization from Nitrate."
   [cfg {:keys [organization-id] :as params}]
diff --git a/backend/src/app/rpc/commands/nitrate.clj b/backend/src/app/rpc/commands/nitrate.clj
index 2103452c17..71a2e93b17 100644
--- a/backend/src/app/rpc/commands/nitrate.clj
+++ b/backend/src/app/rpc/commands/nitrate.clj
@@ -24,7 +24,6 @@
    [app.rpc.nitrate.emails-helper :as neh]
    [app.rpc.nitrate.organization-helper :as noh]
    [app.rpc.notifications :as notifications]
-   [app.tokens :as tokens]
    [app.util.services :as sv]))
 
 
@@ -647,17 +646,11 @@
           {:keys [authorized sso]} (nitrate/sso-session-authorized? cfg organization-id team-id request)]
       (if authorized
         {:authorized true}
-        (if-let [issuer (or (:issuer sso) (:base-url sso))]
-          (let [oidc-provider    (oidc/prepare-org-sso-provider cfg sso)
-                org-id           (or organization-id (:organization-id sso))
-                state-token      (tokens/generate cfg {:iss             "oidc"
-                                                       :dest-url        url
-                                                       :organization-id org-id
-                                                       :issuer          issuer
-                                                       :exp             (ct/in-future "4h")})
-                redirect-uri     (oidc/build-auth-redirect-uri oidc-provider state-token)]
-            {:authorized false
-             :redirect-uri redirect-uri})
+        (if (oidc/org-sso-discovery-uri sso)
+          {:authorized false
+           :redirect-uri (oidc/build-org-sso-auth-redirect-uri cfg sso
+                                                               :dest-url url
+                                                               :organization-id organization-id)}
           {:authorized false
            :redirect-uri nil})))
     {:authorized true}))
diff --git a/backend/src/app/rpc/management/nitrate.clj b/backend/src/app/rpc/management/nitrate.clj
index 9168c0ea63..700cf59cac 100644
--- a/backend/src/app/rpc/management/nitrate.clj
+++ b/backend/src/app/rpc/management/nitrate.clj
@@ -8,11 +8,12 @@
   "Internal Nitrate HTTP RPC API. Provides authenticated access to
   organization management and token validation endpoints."
   (:require
+   [app.auth.oidc :as oidc]
    [app.common.data :as d]
    [app.common.exceptions :as ex]
    [app.common.schema :as sm]
    [app.common.time :as ct]
-   [app.common.types.organization :refer [schema:team-with-organization schema:organization-with-avatar]]
+   [app.common.types.organization :refer [schema:team-with-organization schema:organization-with-avatar schema:nitrate-sso]]
    [app.common.types.profile :refer [schema:profile, schema:basic-profile]]
    [app.common.types.team :refer [schema:team]]
    [app.config :as cf]
@@ -878,6 +879,23 @@ RETURNING id, deleted_at;")
                                   photo-id       (assoc :photo-url       (files/resolve-public-uri photo-id))
                                   owner-photo-id (assoc :owner-photo-url (files/resolve-public-uri owner-photo-id))))))))))))
 
+;; ---- API: check-organization-sso
+
+(def ^:private schema:check-organization-sso-result
+  [:map
+   [:valid ::sm/boolean]])
+
+(sv/defmethod ::check-organization-sso
+  "Validate an organization SSO configuration by generating a login redirect URL.
+  Nitrate calls this while configuring SSO to verify client credentials and OIDC
+  discovery before saving the settings."
+  {::doc/added "2.20"
+   ::sm/params schema:nitrate-sso
+   ::sm/result schema:check-organization-sso-result
+   ::rpc/auth false}
+  [cfg params]
+  {:valid (oidc/is-organization-sso-config-valid? cfg params)})
+
 ;; ---- API: notify-org-sso-change
 (sv/defmethod ::notify-org-sso-change
   "Nitrate notifies that an organization sso values have changed"
@@ -895,3 +913,4 @@ RETURNING id, deleted_at;")
   (when became-active
     (neh/send-organization-setup-sso-emails! cfg organization-id))
   nil)
+
diff --git a/backend/test/backend_tests/auth_oidc_test.clj b/backend/test/backend_tests/auth_oidc_test.clj
index bdf18e5541..7ec2f4bdaf 100644
--- a/backend/test/backend_tests/auth_oidc_test.clj
+++ b/backend/test/backend_tests/auth_oidc_test.clj
@@ -53,3 +53,20 @@
     ;; not silently slip through as if it were the matching string.
     (t/is (= :auto (#'oidc/select-user-info-source :token)))
     (t/is (= :auto (#'oidc/select-user-info-source :userinfo)))))
+
+(t/deftest token-endpoint-errors-detect-valid-client-credentials
+  (let [response {:status 403
+                  :body "{\"error\":\"invalid_grant\",\"error_description\":\"Invalid authorization code\"}"}]
+    (t/is (#'oidc/token-endpoint-valid-client-error? response))
+    (t/is (not (#'oidc/token-endpoint-invalid-client-error? response)))))
+
+(t/deftest token-endpoint-errors-detect-invalid-client-credentials
+  (t/is (#'oidc/token-endpoint-invalid-client-error?
+         {:status 401
+          :body "{\"error\":\"access_denied\",\"error_description\":\"Unauthorized\"}"}))
+  (t/is (#'oidc/token-endpoint-invalid-client-error?
+         {:status 400
+          :body "{\"error\":\"invalid_client\"}"}))
+  (t/is (not (#'oidc/token-endpoint-valid-client-error?
+              {:status 400
+               :body "{\"error\":\"invalid_client\"}"}))))
diff --git a/backend/test/backend_tests/rpc_management_nitrate_test.clj b/backend/test/backend_tests/rpc_management_nitrate_test.clj
index 460471e639..2691514952 100644
--- a/backend/test/backend_tests/rpc_management_nitrate_test.clj
+++ b/backend/test/backend_tests/rpc_management_nitrate_test.clj
@@ -6,6 +6,7 @@
 
 (ns backend-tests.rpc-management-nitrate-test
   (:require
+   [app.auth.oidc :as oidc]
    [app.common.data :as d]
    [app.common.time :as ct]
    [app.common.uuid :as uuid]
@@ -1277,3 +1278,40 @@
     (with-redefs [eml/send! (fn [params] (swap! sent conj params))]
       (management-command-with-nitrate! params))
     (t/is (empty? @sent))))
+
+(t/deftest check-organization-sso-returns-valid-true
+  (let [org-id (uuid/random)
+        out    (with-redefs [oidc/is-organization-sso-config-valid? (constantly true)]
+                 (management-command-with-nitrate!
+                  {::th/type :check-organization-sso
+                   :organization-id org-id
+                   :client-id "test-client"
+                   :client-secret "test-secret"
+                   :base-url "https://idp.example.com"}))]
+    (t/is (th/success? out))
+    (t/is (true? (-> out :result :valid)))))
+
+(t/deftest check-organization-sso-returns-valid-false-on-invalid-config
+  (let [out (management-command-with-nitrate!
+             {::th/type :check-organization-sso
+              :organization-id (uuid/random)
+              :client-id "test-client"
+              :client-secret "test-secret"})]
+    (t/is (th/success? out))
+    (t/is (false? (-> out :result :valid)))))
+
+(t/deftest check-organization-sso-uses-issuer-when-base-url-is-blank
+  (let [org-id (uuid/random)
+        out    (with-redefs [oidc/is-organization-sso-config-valid?
+                             (fn [_cfg sso]
+                               (and (= "test-client" (:client-id sso))
+                                    (= "https://idp.example.com/" (:issuer sso))))]
+                 (management-command-with-nitrate!
+                  {::th/type :check-organization-sso
+                   :organization-id org-id
+                   :client-id "test-client"
+                   :client-secret "test-secret"
+                   :base-url ""
+                   :issuer "https://idp.example.com/"}))]
+    (t/is (th/success? out))
+    (t/is (true? (-> out :result :valid)))))
diff --git a/common/src/app/common/types/organization.cljc b/common/src/app/common/types/organization.cljc
index ca13e7de5b..16c5ab22aa 100644
--- a/common/src/app/common/types/organization.cljc
+++ b/common/src/app/common/types/organization.cljc
@@ -63,3 +63,14 @@
    [:logo [:maybe ::sm/uri]]
    [:avatar-bg-url [:maybe ::sm/uri]]
    [:sso-active {:optional true} [:maybe :boolean]]])
+
+(def schema:nitrate-sso
+  [:map {:title "NitrateOrganizationSso"}
+   [:organization-id ::sm/uuid]
+   [:active {:optional true} [:maybe :boolean]]
+   [:provider {:optional true} [:maybe :string]]
+   [:client-id {:optional true} [:maybe :string]]
+   [:base-url {:optional true} [:maybe :string]]
+   [:client-secret {:optional true} [:maybe :string]]
+   [:issuer {:optional true} [:maybe :string]]
+   [:scopes {:optional true} [:maybe [::sm/set ::sm/text]]]])