Add exchange api endpoint, fix jwt authtoken var type error

Signed-off-by: Asai Neko <sugar@sne.moe>

data/client.go

@@ -32,10 +32,10 @@ func (self *Client) GetClientByClientId(clientId string) (*Client, error) {
 	return &client, nil
 }
 
-func (self *Client) GetDecryptedSecret() (string, error) {
+func (self *Client) GetDecryptedSecret() ([]byte, error) {
 	secretKey := viper.GetString("secrets.client_secret_key")
 	secret, err := cryptography.AESCBCDecrypt(self.ClientSecret, []byte(secretKey))
-	return string(secret), err
+	return secret, err
 }
 
 type ClientParams struct {