fix(server): use protocol forwarded by nginx (#562)

nginx wasn't passing the protocol being used to Django, which was
causing it to treat all requests as unencrypted HTTP. Add config and
make Django respect the forwarded protocol.

Fixes #562

docker/nginx/nginx.conf

@@ -28,6 +28,7 @@ server {
 
         proxy_pass http://shipper;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
         proxy_set_header Host $host;
         proxy_redirect off;
     }

server/config/settings.py

@@ -36,6 +36,9 @@
 
 SECURE_HSTS_SECONDS = int(os.environ.get("SHIPPER_SECURE_HSTS_SECONDS", default=0))
 
+SECURE_PROXY_SSL_HEADER = ("HTTP_X_FORWARDED_PROTO", "https")
+
+
 with open("version.txt") as v_file:
     SHIPPER_VERSION = v_file.readline().rstrip()