The lock granularity is too coarse, causing goroutines to be blocked in high concurrency scenarios.

[Class-public]

func GetOrGenerateKeys(ctx context.Context, r InternalRegistry, m Manager, set, kid, alg string) (private *jose.JSONWebKey, err error) {
	getLock(set).Lock()
	defer getLock(set).Unlock()

	keys, err := m.GetKeySet(ctx, set)
}

[Class-public]

With 400 concurrent requests, this function will blocking and takes 800ms to complete. Should we consider optimizing it?

[Class-public]

@aeneasr