util.go

package auth

import (
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"strings"
)

func randomBytesInHex(count int) (string, error) {
	buf := make([]byte, count)
	_, err := io.ReadFull(rand.Reader, buf)
	if err != nil {
		return "", fmt.Errorf("could not generate %d random bytes: %v", count, err)
	}

	return hex.EncodeToString(buf), nil
}

// isValidAccessToken is a simple validation of the access token
func isValidAccessToken(token string, audience string) error {
	if token == "" {
		return fmt.Errorf("token received is empty")
	}

	encodedClaims := strings.Split(token, ".")[1]
	claimsString, err := base64.RawURLEncoding.DecodeString(encodedClaims)
	if err != nil {
		return err
	}

	claims := Claims{}
	err = json.Unmarshal(claimsString, &claims)
	if err != nil {
		return err
	}

	if claims.Audience == nil {
		return fmt.Errorf("required token field audience is absent")
	}

	// Audience claim of JWT can be a string or an array of strings
	switch aud := claims.Audience.(type) {
	case string:
		if aud == audience {
			return nil
		}
	case []interface{}:
		for _, audItem := range aud {
			if audStr, ok := audItem.(string); ok && audStr == audience {
				return nil
			}
		}
	}

	return fmt.Errorf("invalid JWT token audience field")
}