rewrite and new Hash interface

hash.go

@@ -0,0 +1,86 @@
+package jwt
+
+import (
+	"crypto/sha256"
+	"crypto/sha512"
+	"hash"
+)
+
+const (
+	HS256Name = "HS256"
+	HS384Name = "HS384"
+	HS512Name = "HS512"
+)
+
+// ParseHash returns the Hash type equal to the input string
+func ParseHash(alg string) Hash {
+	switch alg {
+	case HS256Name:
+		return NewHS256()
+	case HS384Name:
+		return NewHS384()
+	case HS512Name:
+		return NewHS512()
+	}
+	return nil
+}
+
+// Hash is the hashsum interface for signing the jwt
+type Hash interface {
+	Hash() hash.Hash
+	Alg() string
+}
+
+// HS256 implements the Hash interface with SHA256
+type HS256 struct{}
+
+// NewHS256 returns a new HS256 instance
+func NewHS256() Hash {
+	return HS256{}
+}
+
+// Alg returns the algorithm name "HS256"
+func (HS256) Alg() string {
+	return HS256Name
+}
+
+// Hash returns a new hash.Hash instance of the SHA256 algorithm
+func (HS256) Hash() hash.Hash {
+	return sha256.New()
+}
+
+// HS384 implements the Hash interface with SHA384
+type HS384 struct{}
+
+// NewHS384 returns a new HS384 instance
+func NewHS384() Hash {
+	return HS384{}
+}
+
+// Alg returns the algorithm name "HS384"
+func (HS384) Alg() string {
+	return HS384Name
+}
+
+// Hash returns a new hash.Hash instance of the SHA384 algorithm
+func (HS384) Hash() hash.Hash {
+	return sha512.New384()
+}
+
+// HS512 implements the Hash interface with SHA512
+type HS512 struct{}
+
+// NewHS512 returns a new HS512 instance
+func NewHS512() Hash {
+	return HS512{}
+}
+
+// Alg returns the algorithm name "HS512"
+func (HS512) Alg() string {
+	return HS512Name
+}
+
+// Hash returns a new hash.Hash instance of the SHA512 algorithm
+func (HS512) Hash() hash.Hash {
+	return sha512.New()
+}