We have a faculty member trying to use Mobile. We are on Moodle 3.1+ (Build: 20160603) and Moodle Mobile local_mobile plugin 3.1.310 (2016050100). We authenticate using CAS, so we use the login via browser window option.
He is able to log in, but immediately gets this error. If he clicks OK, then it takes him into the site.
As far as I know, he's the only person to try to use Mobile other than us admins.
I have debugging enabled for his user, and all I see in the error logs is:
[Thu Aug 18 17:13:49.770420 2016] [proxy_fcgi:error] [pid 30685:tid 140454716679936] [client 220.127.116.11:35902] AH01071: Got error 'PHP message: Default exception handler: A required parameter (username) was missing Debug: \nError code: missingparam\n* line 495 of /lib/setuplib.php: moodle_exception thrown\n* line 552 of /lib/moodlelib.php: call to print_error()\n* line 33 of /login/token.php: call to required_param()\n\n'
The FAQs note that this usually relates to going from https to http or the reverse, but I've verified we are on https the entire time.