Pass real http scheme value to upstream servers

docker/nginx/asciinema.conf

@@ -9,6 +9,11 @@ upstream phoenix-server {
 proxy_cache_path /cache levels=1:2 keys_zone=png_cache:10m max_size=10g
                  inactive=14d use_temp_path=off;
 
+map $http_x_forwarded_proto $real_scheme {
+    default $http_x_forwarded_proto;
+    ''      $scheme;
+}
+
 server {
     listen 80 default_server;
     listen [::]:80 default_server;
@@ -33,7 +38,7 @@ server {
 
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_scheme;
         proxy_set_header Host $http_host;
         proxy_pass http://phoenix-server;
         proxy_redirect off;
@@ -58,7 +63,7 @@ server {
     location @rails {
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_scheme;
         proxy_set_header Host $http_host;
         proxy_pass http://rails-server;
         proxy_redirect off;
@@ -68,7 +73,7 @@ server {
     location @phoenix {
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_scheme;
         proxy_set_header Host $http_host;
         proxy_pass http://phoenix-server;
         proxy_redirect off;