Why does Nginx return headers in lower case?

Question

Nginx

Good afternoon!
Why did Nginx 1.9.13 return HTTP headers in lowercase, how to fix it?

Answer 1

It's okay, you don't need to fix it.
Nginx when enabling HTTP/2 (h2) implements the protocol specification:
SPDY Protocol (Name/Value Header Block)

Header names... must be all lower cases.

Answer 2

HTTP headers are case insensitive