fix(server): accept HTTP/1.1 for backward compatibility (#20639)

Signed-off-by: Alexandre Gaudreault <[email protected]>
Co-authored-by: Michael Crenshaw <[email protected]>

server/server.go

@@ -562,7 +562,11 @@ func (a *ArgoCDServer) Run(ctx context.Context, listeners *Listeners) {
 		// If not matched, we assume that its TLS.
 		tlsl := tcpm.Match(cmux.Any())
 		tlsConfig := tls.Config{
-			NextProtos: []string{"h2"},
+			// Advertise that we support both http/1.1 and http2 for application level communication.
+			// By putting http/1.1 first, we ensure that HTTPS clients will use http/1.1, which is the only
+			// protocol our server supports for HTTPS clients. By including h2 in the list, we ensure that
+			// gRPC clients know we support http2 for their communication.
+			NextProtos: []string{"http/1.1", "h2"},
 		}
 		tlsConfig.GetCertificate = func(info *tls.ClientHelloInfo) (*tls.Certificate, error) {
 			return a.settings.Certificate, nil