diff --git a/src/node/hooks/express/openapi-admin.ts b/src/node/hooks/express/openapi-admin.ts
index 91be2fc48..67e88da8f 100644
--- a/src/node/hooks/express/openapi-admin.ts
+++ b/src/node/hooks/express/openapi-admin.ts
@@ -22,7 +22,29 @@ export const generateAdminDefinition = (): any => ({
       'Distinct from the public /api/{version}/* surface served by /api/openapi.json.',
     version: getEpVersion(),
   },
-  paths: {},
+  paths: {
+    '/admin-auth/': {
+      post: {
+        operationId: 'verifyAdminAccess',
+        summary: 'Verify or establish an admin session',
+        description:
+          'POST with `Authorization: Basic <user:pass>` to log in as an admin ' +
+          '(server sets a session cookie on success). POST with no auth header ' +
+          'to verify an existing admin session cookie. The response body is ' +
+          'always empty; the status code conveys the outcome.',
+        security: [
+          {basicAuth: []},
+          {sessionCookie: []},
+          {},
+        ],
+        responses: {
+          '200': {description: 'Caller is an authenticated admin.'},
+          '401': {description: 'No authentication presented and no admin session exists.'},
+          '403': {description: 'Authenticated, but the user is not an admin.'},
+        },
+      },
+    },
+  },
   components: {
     schemas: {},
     securitySchemes: {
diff --git a/src/tests/backend/specs/openapi-admin.ts b/src/tests/backend/specs/openapi-admin.ts
index 894ae4373..ea8bf7da1 100644
--- a/src/tests/backend/specs/openapi-admin.ts
+++ b/src/tests/backend/specs/openapi-admin.ts
@@ -33,4 +33,26 @@ describe('admin OpenAPI document', function () {
     assert.equal(doc.components.securitySchemes.sessionCookie.type, 'apiKey');
     assert.equal(doc.components.securitySchemes.sessionCookie.in, 'cookie');
   });
+
+  describe('/admin-auth/', function () {
+    it('declares POST with operationId verifyAdminAccess', function () {
+      const op = doc.paths['/admin-auth/']?.post;
+      assert.ok(op, 'POST /admin-auth/ is missing');
+      assert.equal(op.operationId, 'verifyAdminAccess');
+    });
+
+    it('documents responses 200, 401, 403', function () {
+      const responses = doc.paths['/admin-auth/'].post.responses;
+      assert.ok(responses['200'], 'missing 200 response');
+      assert.ok(responses['401'], 'missing 401 response');
+      assert.ok(responses['403'], 'missing 403 response');
+    });
+
+    it('declares security: basicAuth, sessionCookie, anonymous', function () {
+      const security = doc.paths['/admin-auth/'].post.security;
+      assert.ok(Array.isArray(security));
+      const keys = security.map((s: any) => Object.keys(s)[0] ?? '__anon__');
+      assert.deepEqual(keys.sort(), ['__anon__', 'basicAuth', 'sessionCookie'].sort());
+    });
+  });
 });