signature: Use a layered approach for signature verification.

Signature calculation has now moved out from being a package to
top-level as a layered mechanism.

In case of payload calculation with body, go-routines are initiated
to simultaneously write and calculate shasum. Errors are sent
over the writer so that the lower layer removes the temporary files
properly.

signature-jwt.go

@@ -0,0 +1,74 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+import (
+	"strings"
+	"time"
+
+	jwtgo "github.com/dgrijalva/jwt-go"
+	"github.com/minio/minio/pkg/probe"
+	"golang.org/x/crypto/bcrypt"
+)
+
+const jwtAlgorithm = "Bearer"
+
+// JWT - jwt auth backend
+type JWT struct {
+	credential
+}
+
+// Default - each token expires in 10hrs.
+const (
+	tokenExpires time.Duration = 10
+)
+
+// initJWT - initialize.
+func initJWT() *JWT {
+	jwt := &JWT{}
+
+	// Save access, secret keys.
+	jwt.credential = serverConfig.GetCredential()
+
+	// Return.
+	return jwt
+}
+
+// GenerateToken - generates a new Json Web Token based on the incoming user id.
+func (jwt *JWT) GenerateToken(userName string) (string, *probe.Error) {
+	token := jwtgo.New(jwtgo.SigningMethodHS512)
+	// Token expires in 10hrs.
+	token.Claims["exp"] = time.Now().Add(time.Hour * tokenExpires).Unix()
+	token.Claims["iat"] = time.Now().Unix()
+	token.Claims["sub"] = userName
+	tokenString, e := token.SignedString([]byte(jwt.SecretAccessKey))
+	if e != nil {
+		return "", probe.NewError(e)
+	}
+	return tokenString, nil
+}
+
+// Authenticate - authenticates incoming username and password.
+func (jwt *JWT) Authenticate(userName, password string) bool {
+	userName = strings.TrimSpace(userName)
+	password = strings.TrimSpace(password)
+	if userName != jwt.AccessKeyID {
+		return false
+	}
+	hashedPassword, _ := bcrypt.GenerateFromPassword([]byte(jwt.SecretAccessKey), bcrypt.DefaultCost)
+	return bcrypt.CompareHashAndPassword(hashedPassword, []byte(password)) == nil
+}