As I mentioned above, my NC install lives behind a proxy. I’m running nginx inside of a Docker container. When I tail the logs while trying to log in this is what I see.
172.22.1.104 - - [13/May/2019:11:21:16 -0600] "GET /index.php/login/flow/grant?clientIdentifier=&stateToken=qdHVWU9JZFVzzdtMiU9BiNZUMvgvcKCtgfxHOm8oKIDnk34c7CW4NSKxeL4SXask HTTP/1.1" 301 185 "-" "Mozilla/5.0 (Macintosh) mirall/2.5.1final (build 20181204) (Nextcloud)" "-"
172.22.1.104 - - [13/May/2019:11:21:16 -0600] "GET /index.php/login/flow/grant?clientIdentifier=&stateToken=qdHVWU9JZFVzzdtMiU9BiNZUMvgvcKCtgfxHOm8oKIDnk34c7CW4NSKxeL4SXask HTTP/1.1" 200 7444 "-" "Mozilla/5.0 (Macintosh) mirall/2.5.1final (build 20181204) (Nextcloud)" "-"
172.22.1.104 - - [13/May/2019:11:21:16 -0600] "GET /index.php/core/js/oc.js?v=d3dc0e9b HTTP/1.1" 200 5595 "-" "Mozilla/5.0 (Macintosh) mirall/2.5.1final (build 20181204) (Nextcloud)" "-"
172.22.1.104 - - [13/May/2019:11:21:33 -0600] "POST /index.php/login/flow HTTP/1.1" 301 185 "-" "Mozilla/5.0 (Macintosh) mirall/2.5.1final (build 20181204) (Nextcloud)" "-"
172.22.1.104 - - [13/May/2019:11:21:34 -0600] "GET /index.php/login/flow HTTP/1.1" 200 7981 "-" "Mozilla/5.0 (Macintosh) mirall/2.5.1final (build 20181204) (Nextcloud)" "-"
172.22.1.104 - - [13/May/2019:11:21:34 -0600] "GET /index.php/core/js/oc.js?v=d3dc0e9b HTTP/1.1" 200 5595 "-" "Mozilla/5.0 (Macintosh) mirall/2.5.1final (build 20181204) (Nextcloud)" "-"
From what I can tell this all looks good. Not sure what else to try to get this working.