• Gitea version (or commit ref): f9a5cc4
• Git version: 2.15.0
• Operating system: Ubuntu Linux host but running in Docker with de standard latest image
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No -> the Dropbox login is not available
  • Not relevant
• Log gist:
  I'm not sure what you're talking about but this looks to display the error:

[Macaron] 2018-01-31 11:50:35: Started GET /user/oauth2/dropbox for 145.239.14.126 [Macaron] 2018-01-31 11:50:35: Completed GET /user/oauth2/dropbox 307 Temporary Redirect in 1.948058ms [Macaron] 2018-01-31 11:50:46: Started GET /user/oauth2/dropbox/callback?state=b809e90d-bfeb-48ec-9f4f-c591ed257bcc&code=t3gRdKRB6qgAAAAAAAAA3D9YWFDz1xUOvYjzvKtLzCU for 145.239.14.126 [Macaron] 2018-01-31 11:50:48: Completed GET /user/oauth2/dropbox/callback?state=b809e90d-bfeb-48ec-9f4f-c591ed257bcc&code=t3gRdKRB6qgAAAAAAAAA3D9YWFDz1xUOvYjzvKtLzCU 404 Not Found in 1.195064719s [Macaron] 2018-01-31 11:50:48: Started GET /img/500.png for 145.239.14.126 

Description

When clicking on the Dropbox logo the navigation goes to the login page of Dropbox and valide the login.
But when I get back to the Gitea login page I get the error 500.

All other external login I deployed are working great.

Screenshots