server {
listen       80;
server_name www.mydomain.com;
location / {
  proxy_pass http://my-backend;
}

location /app/ {
  rewrite ^/(.*)$ "/\#$1" break;
  proxy_pass http://my-backend;
}

Bad request For request 'GET /%23app/1' [Illegal character in path at index 1: /%23app/1]