.travis, build: autodelete old unstable archives (#13867)

This commit adds a build step to travis to auto-delete unstable archives older than
14 days (our regular release schedule) from Azure via ci.go purge.

The commit also pulls in the latest Azure storage code, also switching over from
the old import path (github.com/Azure/azure-sdk-for-go) to the new split one
(github.com/Azure/azure-storage-go).

vendor/github.com/dgrijalva/jwt-go/rsa.go

@@ -0,0 +1,100 @@
+package jwt
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+)
+
+// Implements the RSA family of signing methods signing methods
+type SigningMethodRSA struct {
+	Name string
+	Hash crypto.Hash
+}
+
+// Specific instances for RS256 and company
+var (
+	SigningMethodRS256 *SigningMethodRSA
+	SigningMethodRS384 *SigningMethodRSA
+	SigningMethodRS512 *SigningMethodRSA
+)
+
+func init() {
+	// RS256
+	SigningMethodRS256 = &SigningMethodRSA{"RS256", crypto.SHA256}
+	RegisterSigningMethod(SigningMethodRS256.Alg(), func() SigningMethod {
+		return SigningMethodRS256
+	})
+
+	// RS384
+	SigningMethodRS384 = &SigningMethodRSA{"RS384", crypto.SHA384}
+	RegisterSigningMethod(SigningMethodRS384.Alg(), func() SigningMethod {
+		return SigningMethodRS384
+	})
+
+	// RS512
+	SigningMethodRS512 = &SigningMethodRSA{"RS512", crypto.SHA512}
+	RegisterSigningMethod(SigningMethodRS512.Alg(), func() SigningMethod {
+		return SigningMethodRS512
+	})
+}
+
+func (m *SigningMethodRSA) Alg() string {
+	return m.Name
+}
+
+// Implements the Verify method from SigningMethod
+// For this signing method, must be an rsa.PublicKey structure.
+func (m *SigningMethodRSA) Verify(signingString, signature string, key interface{}) error {
+	var err error
+
+	// Decode the signature
+	var sig []byte
+	if sig, err = DecodeSegment(signature); err != nil {
+		return err
+	}
+
+	var rsaKey *rsa.PublicKey
+	var ok bool
+
+	if rsaKey, ok = key.(*rsa.PublicKey); !ok {
+		return ErrInvalidKeyType
+	}
+
+	// Create hasher
+	if !m.Hash.Available() {
+		return ErrHashUnavailable
+	}
+	hasher := m.Hash.New()
+	hasher.Write([]byte(signingString))
+
+	// Verify the signature
+	return rsa.VerifyPKCS1v15(rsaKey, m.Hash, hasher.Sum(nil), sig)
+}
+
+// Implements the Sign method from SigningMethod
+// For this signing method, must be an rsa.PrivateKey structure.
+func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string, error) {
+	var rsaKey *rsa.PrivateKey
+	var ok bool
+
+	// Validate type of key
+	if rsaKey, ok = key.(*rsa.PrivateKey); !ok {
+		return "", ErrInvalidKey
+	}
+
+	// Create the hasher
+	if !m.Hash.Available() {
+		return "", ErrHashUnavailable
+	}
+
+	hasher := m.Hash.New()
+	hasher.Write([]byte(signingString))
+
+	// Sign the string and return the encoded bytes
+	if sigBytes, err := rsa.SignPKCS1v15(rand.Reader, rsaKey, m.Hash, hasher.Sum(nil)); err == nil {
+		return EncodeSegment(sigBytes), nil
+	} else {
+		return "", err
+	}
+}