Adding security key not possible

[pheerai]

• Gitea version (or commit ref): 1.5.3
• Git version: 2.11.0
• Operating system: Linux 4.9.0-8-amd64 #1 SMP Debian 4.9.110-3+deb9u6 (2018-10-08) x86_64 GNU/Linux
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No (but that one throws an HTTP 500 on registering, so no real possibility for that)
  • Not relevant
• Log gist: https://gist.github.com/pheerai/5076734a2e962fcb7246810f869a491a
  (Note that the last line is unrelated to the issue and seems to be triggered by some sweep scan)

Description

On my setup using a gitea instance behind an NGinx reverse proxy using a root URL of the form https://example.org/git/ I cannot add a security key.

This seems to emerge from the fact that the URL of the security key form does not respect the fiven root (it is https://example.org/user/settings/security/u2f/request_register instead of https://example.org/git/user/settings/security/u2f/request_register

Screenshots

This is the debug output of the request that occurs in the moment I click the "add security key" button. It fails as the intermediate /git is missing.