piotrkowalczuk/mnemosyne

package mnemosyne

import (
    "crypto/rand"
    "encoding/hex"
    "io"

    "golang.org/x/crypto/sha3"
    "golang.org/x/net/context"
)

const (
    // AccessTokenMetadataKey is used by Mnemosyne to retrieve session token from gRPC metadata object.
    AccessTokenMetadataKey = "authorization"
)

type key struct{}

var accessTokenContextKey = key{}

// NewAccessTokenContext returns a new Context that carries token value.
func NewAccessTokenContext(ctx context.Context, at string) context.Context {
    return context.WithValue(ctx, accessTokenContextKey, at)
}

// AccessTokenFromContext returns the token value stored in context, if any.
func AccessTokenFromContext(ctx context.Context) (string, bool) {
    at, ok := ctx.Value(accessTokenContextKey).(string)

    return at, ok
}

// RandomAccessToken generate Access Token with given key and generated hash of length 64.
func RandomAccessToken() (string, error) {
    buf, err := generateRandomBytes(128)
    if err != nil {
        return "", err
    }

    // A hash needs to be 64 bytes long to have 256-bit collision resistance.
    hash := make([]byte, 64)
    // Compute a 64-byte hash of buf and put it in h.
    sha3.ShakeSum256(hash, buf)
    hash2 := make([]byte, hex.EncodedLen(len(hash)))
    hex.Encode(hash2, hash)
    return string(hash2), nil
}

func generateRandomBytes(length int) ([]byte, error) {
    k := make([]byte, length)
    if _, err := io.ReadFull(rand.Reader, k); err != nil {
        return nil, err
    }
    return k, nil
}