How to set the ~/ path in Asp.net core - url

Question

This answer: https://stackoverflow.com/a/10469032/3958875 indicates that the ~/ in urls will be set to the actual root of the application if the application is in a virtual directory.
However, I can't seem to find how I can set this path/value.
For example, I have the app behind nginx reverse proxy, so that the root of the app is here: www.mywebsite.com/app1/
Therefore I want all ~/ to be expanded to app1/. How can I accomplish this?
I tried app.UsePathBase("/app1"); in the Configure method in Startup.cs, which didn't seem to do anything.
My nginx config is like:
server {
server_name: apps.mywebsite.com
location / {
...
}
location /app1/ {
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://localhost:5000/;
}
#Https stuff ...
}
Am I missing something that I can pass to asp.net from nginx?

Answer 1

~ will expand to the content root. That is the effectively the path base that is configured for an incoming request.
What app.UsePathBase() does is tell the application that when the incoming request starts with the specified prefix, then that will be used as the path base. So in your case, when the incoming request starts with /app1, then /app1 will be the path base, and ~ will be expanded to /app1.
If you look at your reverse proxy configuration, you can see however that the path /app1 is not actually passed to the application:
location /app1/ {
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://localhost:5000/;
}
So when you access the page at /app1/foo, the request path that gets passed to the application will be just /foo. So the /app1 path base isn’t seen by the application and it won’t be able to respond appropriately.
What you need to do instead is actually pass the full path to the application. You then use app.UsePathBase() to configure that path base so that it gets interpreted correctly:
location /app1/ {
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://localhost:5000/app1/;
}
app.UsePathBase("/app1");
Now, incoming requests at /app1/foo will translate to the same path within your application, the /app1 path base will be used and ~ should expand properly to /app1.

Answer 2

Turns out the error is indeed in my nginx configuration.
By following the documentation on asp and nginx here: https://learn.microsoft.com/en-us/aspnet/core/host-and-deploy/linux-nginx?view=aspnetcore-2.2
I changed my nginx config to:
...
location /app1/ {
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://localhost:5000;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection keep-alive;
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
}
...
And ~ expanded properly.