diff --git a/news/1303.feature b/news/1303.feature
new file mode 100644
index 0000000000..7100014e67
--- /dev/null
+++ b/news/1303.feature
@@ -0,0 +1,2 @@
+Logging in to or out of Plone classic or the API does the same in the other.
+[rpatterson]
diff --git a/src/plone/restapi/services/auth/login.py b/src/plone/restapi/services/auth/login.py
index b0d65c6648..b51962dcb9 100644
--- a/src/plone/restapi/services/auth/login.py
+++ b/src/plone/restapi/services/auth/login.py
@@ -28,8 +28,10 @@ def reply(self):
         if "IDisableCSRFProtection" in dir(plone.protect.interfaces):
             alsoProvides(self.request, plone.protect.interfaces.IDisableCSRFProtection)
 
-        userid = data["login"]
-        password = data["password"]
+        # Also add credentials to the request for other code that depends on it.  In
+        # particular, the PAS cookie authentication plugin depends on `__ac_password`.
+        userid = self.request.form["__ac_name"] = data["login"]
+        password = self.request.form["__ac_password"] = data["password"]
         uf = self._find_userfolder(userid)
 
         if uf is not None: