I have a custom app that I uploaded as a static resource. I have tested that it works if I navigate directly to it. 
The problem is when I use that URL in a lightning container in a component. When I checked network traffic, I found that

1. instead of https://my-dev-ed.lightning.force.com/resource/myapp/default.html there is a request to https://my-dev-ed--c.container.lightning.com/lcc/myapp/default.html
2. The response to this request is 403 Forbidden

I truly appreciate your help.

I have a custom app that I uploaded as a static resource. I have tested that it works if I navigate directly to it. 
The problem is when I use that URL in a lightning container in a component. When I checked network traffic, I found that

1. instead of https://my-dev-ed.lightning.force.com/resource/myapp/default.html there is a request to https://my-dev-ed--c.container.lightning.com/lcc/myapp/default.html
2. The response to this request is 403 Forbidden

I truly appreciate your help.