mutex around signing method registration. shouldn't matter, but couldn't hurt

signing_method.go

@@ -1,6 +1,11 @@
 package jwt
 
+import (
+	"sync"
+)
+
 var signingMethods = map[string]func() SigningMethod{}
+var signingMethodLock = new(sync.RWMutex)
 
 // Implement SigningMethod to add new methods for signing or verifying tokens.
 type SigningMethod interface {
@@ -12,11 +17,17 @@ type SigningMethod interface {
 // Register the "alg" name and a factory function for signing method.
 // This is typically done during init() in the method's implementation
 func RegisterSigningMethod(alg string, f func() SigningMethod) {
+	signingMethodLock.Lock()
+	defer signingMethodLock.Unlock()
+
 	signingMethods[alg] = f
 }
 
 // Get a signing method from an "alg" string
 func GetSigningMethod(alg string) (method SigningMethod) {
+	signingMethodLock.RLock()
+	defer signingMethodLock.RUnlock()
+
 	if methodF, ok := signingMethods[alg]; ok {
 		method = methodF()
 	}