Let's say we can a blog hosted as Wordpress.com but visible on our custom domain in subpath due to SEO.
WordPress.com supports changing domain/subdomain but not path.

We could either make our own installation, change hosting provier or make nginx proxy with URL rewrites.

- WP blog: https://example.wordpress.com/
- Desired site: http://example.com/blog/

This tutorial is inpsired by http://marsbard.github.io/2016-07-30-replace-urls-behind-nginx-reverse-proxy/.

Nginx needs the [ngx_http_sub_module](https://nginx.org/en/docs/http/ngx_http_sub_module.html).
You can check with: `nginx -V`.

`nginx.conf` - put into the `server` section and restart:

```
# nginx rule to make a wordpress.com site visible at subpath of our domain.
# Wordpress.com allows setting domain/subdomain, but not custom path.
# We have to proxy requests and rewrite base URLs rendered by WP to our site.
# Original base URL: https://example.wordpress.com/
# User facing base URL: https://example.com/blog/
# For administration better use the original domain.

# path on our site (visible to users)
location /blog/ {
  # request get proxied to this site (hosted by wordpress.com)
  proxy_pass https://example.wordpress.com/;
  proxy_set_header X-Forwarded-Host $host;
  proxy_set_header X-Forwarded-Proto $scheme;
  # disable compression to make substitution work
  proxy_set_header Accept-Encoding "";

  # substitute URL rendered by wordpress.com to our location
  # http://marsbard.github.io/2016-07-30-replace-urls-behind-nginx-reverse-proxy/
  # plain URL:
  sub_filter 'https://example.wordpress.com' '$scheme://$host/blog';
  # escaped in JS:
  sub_filter 'https:\/\/example.wordpress.com' '$scheme:\/\/$host\/blog';
  # redirect in JS in URL parameters:
  sub_filter 'redirect_to=https%3A%2F%2Fexample.wordpress.com%2F' 'redirect_to=$scheme%3A%2F%2F$host%2Fblog%2F';
  # replace many times
  sub_filter_once off;
  # keep the last modified header
  sub_filter_last_modified on;
}
```

Various places where base URL appears in plain or escaped forms:
```
https://example.wordpress.com
https:\/\/example.wordpress.com
https:\/\/example.wordpress.com\/wp-login.php?redirect_to=https%3A%2F%2Fexample.wordpress.com%2F
```