Add token generation using go macaroon (#437)

* Add Go macaroon library

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

* Add macaroon generation and serialization, for login token.

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

* Remove copyright, trim empty lines

* Make Serialize functions private

* Fix typos

vendor/src/github.com/go-macaroon/macaroon/crypto_test.go

@@ -0,0 +1,66 @@
+package macaroon
+
+import (
+	"crypto/rand"
+	"fmt"
+
+	"golang.org/x/crypto/nacl/secretbox"
+	gc "gopkg.in/check.v1"
+)
+
+type cryptoSuite struct{}
+
+var _ = gc.Suite(&cryptoSuite{})
+
+var testCryptKey = &[hashLen]byte{'k', 'e', 'y'}
+var testCryptText = &[hashLen]byte{'t', 'e', 'x', 't'}
+
+func (*cryptoSuite) TestEncDec(c *gc.C) {
+	b, err := encrypt(testCryptKey, testCryptText, rand.Reader)
+	c.Assert(err, gc.IsNil)
+	t, err := decrypt(testCryptKey, b)
+	c.Assert(err, gc.IsNil)
+	c.Assert(string(t[:]), gc.Equals, string(testCryptText[:]))
+}
+
+func (*cryptoSuite) TestUniqueNonces(c *gc.C) {
+	nonces := make(map[string]struct{})
+	for i := 0; i < 100; i++ {
+		nonce, err := newNonce(rand.Reader)
+		c.Assert(err, gc.IsNil)
+		nonces[string(nonce[:])] = struct{}{}
+	}
+	c.Assert(nonces, gc.HasLen, 100, gc.Commentf("duplicate nonce detected"))
+}
+
+type ErrorReader struct{}
+
+func (*ErrorReader) Read([]byte) (int, error) {
+	return 0, fmt.Errorf("fail")
+}
+
+func (*cryptoSuite) TestBadRandom(c *gc.C) {
+	_, err := newNonce(&ErrorReader{})
+	c.Assert(err, gc.ErrorMatches, "^cannot generate random bytes:.*")
+
+	_, err = encrypt(testCryptKey, testCryptText, &ErrorReader{})
+	c.Assert(err, gc.ErrorMatches, "^cannot generate random bytes:.*")
+}
+
+func (*cryptoSuite) TestBadCiphertext(c *gc.C) {
+	buf := randomBytes(nonceLen + secretbox.Overhead)
+	for i := range buf {
+		_, err := decrypt(testCryptKey, buf[0:i])
+		c.Assert(err, gc.ErrorMatches, "message too short")
+	}
+	_, err := decrypt(testCryptKey, buf)
+	c.Assert(err, gc.ErrorMatches, "decryption failure")
+}
+
+func randomBytes(n int) []byte {
+	buf := make([]byte, n)
+	if _, err := rand.Reader.Read(buf); err != nil {
+		panic(err)
+	}
+	return buf
+}