feat: update nginx configuration to use forwarded_proto variable and add .env.example for local setup

frontend/nginx.conf

@@ -1,3 +1,8 @@
+map $http_x_forwarded_proto $forwarded_proto {
+    default $http_x_forwarded_proto;
+    "" $scheme;
+}
+
 server {
     listen 80;
     server_name localhost;
@@ -13,7 +18,7 @@ server {
         proxy_set_header Host $host;
         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 $forwarded_proto;
     }
 
     # Spring Security OAuth2 login initiation
@@ -22,7 +27,7 @@ server {
         proxy_set_header Host $host;
         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 $forwarded_proto;
     }
 
     # Spring Security OAuth2 callback (authorization code)
@@ -31,7 +36,7 @@ server {
         proxy_set_header Host $host;
         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 $forwarded_proto;
     }
 
     # Spring Security logout endpoint
@@ -40,7 +45,7 @@ server {
         proxy_set_header Host $host;
         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 $forwarded_proto;
     }
 
     error_page 500 502 503 504 /50x.html;