MM-63195: Enforce MFA requirement for non-self requests (#30290)

https://mattermost.atlassian.net/browse/MM-63195

```release-note
NONE
```

server/channels/api4/user.go

@@ -1650,7 +1650,12 @@ func updateUserMfa(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if user, err := c.App.GetUser(c.Params.UserId); err == nil {
+	if appErr := c.App.MFARequired(c.AppContext); !c.AppContext.Session().Local && c.AppContext.Session().UserId != c.Params.UserId && appErr != nil {
+		c.Err = appErr
+		return
+	}
+
+	if user, appErr := c.App.GetUser(c.Params.UserId); appErr == nil {
 		audit.AddEventParameterAuditable(auditRec, "user", user)
 	}
 
@@ -1672,8 +1677,8 @@ func updateUserMfa(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	c.LogAudit("attempt")
 
-	if err := c.App.UpdateMfa(c.AppContext, activate, c.Params.UserId, code); err != nil {
+	if appErr := c.App.UpdateMfa(c.AppContext, activate, c.Params.UserId, code); appErr != nil {
-		c.Err = err
+		c.Err = appErr
 		return
 	}
 

server/channels/api4/user_test.go

@@ -3443,20 +3443,44 @@ func TestUpdateUserMfa(t *testing.T) {
 	defer th.TearDown()
 
 	th.App.Srv().SetLicense(model.NewTestLicense("mfa"))
+	t.Run("Without enforcing", func(t *testing.T) {
 		th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.EnableMultifactorAuthentication = true })
 
 		session, _ := th.App.GetSession(th.Client.AuthToken)
 		session.IsOAuth = true
 		th.App.AddSessionToCache(session)
 
+		defer th.Server.Platform().ClearUserSessionCacheLocal(th.BasicUser.Id)
+
 		resp, err := th.Client.UpdateUserMfa(context.Background(), th.BasicUser.Id, "12345", false)
 		require.Error(t, err)
 		CheckForbiddenStatus(t, resp)
 
 		th.TestForSystemAdminAndLocal(t, func(t *testing.T, client *model.Client4) {
-		_, err = client.UpdateUserMfa(context.Background(), th.BasicUser.Id, "12345", false)
+			_, err := client.UpdateUserMfa(context.Background(), th.BasicUser.Id, "12345", false)
 			require.NoError(t, err)
 		})
+	})
+
+	t.Run("Enforcing", func(t *testing.T) {
+		th.App.UpdateConfig(func(cfg *model.Config) {
+			*cfg.ServiceSettings.EnableMultifactorAuthentication = true
+			*cfg.ServiceSettings.EnforceMultifactorAuthentication = true
+		})
+
+		resp, err := th.Client.UpdateUserMfa(context.Background(), th.BasicUser.Id, "12345", false)
+		require.NoError(t, err)
+		CheckOKStatus(t, resp)
+
+		resp, err = th.LocalClient.UpdateUserMfa(context.Background(), th.BasicUser.Id, "12345", false)
+		require.NoError(t, err)
+		CheckOKStatus(t, resp)
+
+		resp, err = th.SystemAdminClient.UpdateUserMfa(context.Background(), th.BasicUser.Id, "12345", false)
+		require.Error(t, err)
+		CheckForbiddenStatus(t, resp)
+		CheckErrorID(t, err, "api.context.mfa_required.app_error")
+	})
 }
 
 func TestUserLoginMFAFlow(t *testing.T) {