Our instance worked under HTTPS, see this package:
server.xml:
https://bitbucket.org/lelik/atlassian-stash-deb/src/15746d63c675bf8058d4b3176804604e3ea39cbd/etc/stash/server.xml?at=master

nginx config for HTTP:
https://bitbucket.org/lelik/atlassian-stash-deb/src/15746d63c675bf8058d4b3176804604e3ea39cbd/etc/nginx/sites-available/stash?at=master

nginx config for HTTPS:
https://bitbucket.org/lelik/atlassian-stash-deb/src/15746d63c675bf8058d4b3176804604e3ea39cbd/etc/nginx/sites-available/stash-ssl?at=master

In Server Settings URL of Stash Server is "https://stash.acme.com"

In clone popup show always:
http://user@stash.acme.com

Git does not handle 302 redirect in this case and fail on fetch/clone.