auth: remove contextwithHTTPClient

Setting a custom Transport with no ability for the caller to configure
it breaks the ability to configure an http proxy, while the default
behavior via http.DefaultTransport is to support it (via env),
see https://pkg.go.dev/net/http#RoundTripper.

This was added because Spotify didn't support HTTP/2 in 2017, but it
does now. Also, Go net/http should auto negotiate better.

auth/auth.go

@@ -2,7 +2,6 @@ package spotifyauth
 
 import (
 	"context"
-	"crypto/tls"
 	"errors"
 	"net/http"
 	"os"
@@ -140,17 +139,6 @@ func New(opts ...AuthenticatorOption) *Authenticator {
 	return a
 }
 
-// contextWithHTTPClient returns a context with a value set to override the oauth2 http client as Spotify does not
-// support HTTP/2
-//
-// see: https://github.com/zmb3/spotify/issues/20
-func contextWithHTTPClient(ctx context.Context) context.Context {
-	tr := &http.Transport{
-		TLSNextProto: map[string]func(authority string, c *tls.Conn) http.RoundTripper{},
-	}
-	return context.WithValue(ctx, oauth2.HTTPClient, &http.Client{Transport: tr})
-}
-
 // ShowDialog forces the user to approve the app, even if they have already done so.
 // Without this, users who have already approved the app are immediately redirected to the redirect uri.
 var ShowDialog = oauth2.SetAuthURLParam("show_dialog", "true")
@@ -180,17 +168,17 @@ func (a Authenticator) Token(ctx context.Context, state string, r *http.Request,
 	if actualState != state {
 		return nil, errors.New("spotify: redirect state parameter doesn't match")
 	}
-	return a.config.Exchange(contextWithHTTPClient(ctx), code, opts...)
+	return a.config.Exchange(ctx, code, opts...)
 }
 
 // Exchange is like Token, except it allows you to manually specify the access
 // code instead of pulling it out of an HTTP request.
 func (a Authenticator) Exchange(ctx context.Context, code string, opts ...oauth2.AuthCodeOption) (*oauth2.Token, error) {
-	return a.config.Exchange(contextWithHTTPClient(ctx), code, opts...)
+	return a.config.Exchange(ctx, code, opts...)
 }
 
 // Client creates a *http.Client that will use the specified access token for its API requests.
 // Combine this with spotify.HTTPClientOpt.
 func (a Authenticator) Client(ctx context.Context, token *oauth2.Token) *http.Client {
-	return a.config.Client(contextWithHTTPClient(ctx), token)
+	return a.config.Client(ctx, token)
 }