A simpler way to add Bearer token when testing with devise-jwt?

Question

I'm doing request specs. We use devise-jwt to do authentication, so I need to put the Authorization header in every request which needs permission to call.

I read the document of Devise JWT so I know I can use

 user = fetch_my_user()
 headers = { 'Accept' => 'application/json', 'Content-Type' => 'application/json' }
 # This will add a valid token for `user` in the `Authorization` header
 auth_headers = Devise::JWT::TestHelpers.auth_headers(headers, user)

 get '/my/end_point', headers: auth_headers

However, Devise::JWT::TestHelpers.auth_headers, seems just merge {"Authorization" => "Bearer JWT-TOKEN"} into the passed-in headers hash.
Why I cannot have directly the hash {"Authorization" => "Bearer JWT-TOKEN"}, can I?

Or my real question is why it needs Warden::JWTAuth::HeaderParser.to_headers inside the auth_headers method? what's that used for?

Warden::JWTAuth::HeaderParser.to_headers(headers, token)