Reverse Proxy setup guide (#600)

I've added a more comprehensive guide to set up Reverse Proxies.

So far I've added nginx configuration, I'm also planning to add apache configuration later on.

Reviewed-on: https://codeberg.org/forgejo/docs/pulls/600
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Kwonunn <kwonunnx@gmail.com>
Co-committed-by: Kwonunn <kwonunnx@gmail.com>
(cherry picked from commit c1b7969c1d)

docs/admin/reverse-proxy.md

@@ -4,6 +4,200 @@ license: 'Apache-2.0'
 origin_url: 'https://github.com/go-gitea/gitea/blob/e865de1e9d65dc09797d165a51c8e705d2a86030/docs/content/usage/authentication.en-us.md'
 ---
 
+You may wish to place your Forgejo instance behind a reverse proxy. A reverse proxy is a server that accepts requests from the outside and routes them to internal services, like Forgejo.
+
+## nginx
+
+### Basic HTTP
+
+To set up a basic HTTP reverse proxy in nginx, create a file `forgejo.conf` in `/etc/nginx/conf.d` and add the following configuration:
+
+```conf
+server {
+    listen 80; # Listen on IPv4 port 80
+    listen [::]:80; # Listen on IPv6 port 80
+
+    server_name git.example.com; # Change this to the server domain name.
+
+    location / {
+        proxy_pass http://127.0.0.1:3000; # Port 3000 is the default Forgejo port
+
+        proxy_set_header Connection $http_connection;
+        proxy_set_header Upgrade $http_upgrade;
+        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;
+
+        client_max_body_size 512M;
+    }
+}
+```
+
+Make sure to reload/restart nginx after chaning the configuration.
+
+### HTTP with a subpath
+
+If you want to serve Forgejo on a subpath, e.g. on `http://example.com/forgejo`, use the following configuration:
+
+```conf
+server {
+    listen 80; # Listen on IPv4 port 80
+    listen [::]:80; # Listen on IPv6 port 80
+
+    server_name git.example.com; # Change this to the server domain name.
+
+    location /forgejo/ { # Replace forgejo here with your subpath
+        rewrite ^ $request_uri;
+        rewrite ^/forgejo(/.*) $1 break;
+        return 400;
+        proxy_pass http://127.0.0.1:3000$uri;
+
+        proxy_set_header Connection $http_connection;
+        proxy_set_header Upgrade $http_upgrade;
+        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 $scheme;
+
+        client_max_body_size 512M;
+    }
+}
+```
+
+Make sure to set the Forgejo `ROOT_URL` configuration key to the URL _with_ the subpath, otherwise links generated by Forgejo will be broken.
+
+### HTTPS
+
+When using a reverse proxy, it's usually easier to let the proxy handle HTTPS. It's easy to set up HTTPS on nginx.
+
+#### HTTPS with Certbot
+
+To set up HTTPS with Certbot, first set up an HTTP reverse proxy with the configuration above and ensure that it works as expected. To use HTTPS you need to have a domain name.
+
+Then, install [certbot](https://certbot.eff.org/). When running certbot, select the domain name that your Forgejo instance is hosted under, and choose automatic installation. This should automatically set up HTTPS on port 443 and a redirect on the old port 80.
+
+You may wish to change the `ROOT_URL` configuration key to the HTTPS protocol so links generated by Forgejo automatically use HTTPS.
+
+#### HTTPS with manually installed certificates
+
+If you have obtained certificates from elsewhere or have chosen not to let certbot automatically install them, make the following changes to the configuration file:
+
+**Change the listening ports**
+
+Change the lines
+
+```conf
+listen 80;
+listen [::]:80;
+```
+
+to
+
+```conf
+listen 443 ssl http2;
+listen [::]:443 ssl http2;
+```
+
+**Add the SSL certificate information**
+
+Generate an SSL configuration at [mozilla](https://ssl-config.mozilla.org/#server=nginx), and add the SSL parameters to your configuration file. Make sure to replace the paths in the example with paths to your certificate files.
+
+**Add a redirect from HTTP**
+
+Outside the server block, add this redirection block:
+
+```conf
+server {
+    listen 80 default_server;
+    listen [::]:80 default_server;
+
+    location / {
+        return 301 https://$host$request_uri;
+    }
+}
+```
+
+This will redirect anyone visiting the HTTP site to the HTTPS site.
+
+## Apache
+
+### Basic HTTP
+
+To set up a basic HTTP proxy in Apache, create a file `100-forgejo.conf` in `/etc/apache2/sites-available` and add the following configuration:
+
+```xml
+<VirtualHost *:80>
+    ServerName git.example.com
+
+    ProxyPreserveHost On
+    ProxyRequests off
+    AllowEncodedSlashes NoDecode
+    ProxyPass / http://127.0.0.1:3000/ nocanon
+</VirtualHost>
+```
+
+Next, enable the site with `a2ensite 100-forgejo.conf` and enable the proxy modules with `a2enmod proxy proxy_http`. Finally, restart the apache server.
+
+### HTTP with a subpath
+
+If you want to serve Forgejo on a subpath, e.g. on `http://example.com/forgejo`, use the following configuration:
+
+```xml
+<VirtualHost *:80>
+    ServerName git.example.com
+
+    ProxyPreserveHost On
+    ProxyRequests off
+    AllowEncodedSlashes NoDecode
+    ProxyPass /forgejo http://127.0.0.1:3000/ nocanon # Change /forgejo here to your desired subpath.
+</VirtualHost>
+```
+
+Make sure to set the Forgejo `ROOT_URL` configuration key to the URL _with_ the subpath, otherwise links generated by Forgejo will be broken.
+
+### HTTPS
+
+When using a reverse proxy, it's usually easier to let the proxy handle HTTPS. It's easy to set up HTTPS on apache.
+
+#### HTTPS with Certbot
+
+To set up HTTPS with Certbot, first set up an HTTP reverse proxy with the configuration above and ensure that it works as expected. To use HTTPS you need to have a domain name.
+
+Then, install [certbot](https://certbot.eff.org/). When running certbot, select the domain name that your Forgejo instance is hosted under, and choose automatic installation. This should automatically set up HTTPS on port 443 and a redirect on the old port 80.
+
+You may wish to change the `ROOT_URL` configuration key to the HTTPS protocol so links generated by Forgejo automatically use HTTPS.
+
+#### HTTPS with manually installed certificates
+
+If you have obtained certificates from elsewhere or have chosen not to let certbot automatically install them, make the following changes to the configuration file:
+
+**Change the listening ports**
+
+Change `<VirtualHost *:80>` to `<VirtualHost *:443>`.
+
+**Add the SSL certificate information**
+
+Generate an SSL configuration at [mozilla](https://ssl-config.mozilla.org/#server=apache), and add the SSL parameters to your configuration file. Make sure to replace the paths in the example with paths to your certificate files.
+
+**Add a redirect from HTTP**
+
+Outside the `VirtualHost *:443`, add this configuration:
+
+```conf
+<VirtualHost *:80>
+    ServerName git.example.com
+
+    RewriteEngine on
+    RewriteCond %{SERVER_NAME} =git.example.com
+    RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
+</VirtualHost>
+```
+
+This will redirect anyone visiting the HTTP site to the HTTPS site.
+
+## Proxy Authentication
+
 Forgejo supports Reverse Proxy Header authentication, it will read headers as a trusted login user name or user email address. This hasn't been enabled by default, you can enable it with
 
 ```ini