The signature string * * * has four lines, each with one parameter. The line ends with \n (line feed, ASCII code value 0x0A), including the last line. If the parameter itself ends in \n, an additional \n is required.

2. Calculate the signature value

The merchant's private key is used to sign * the string to be signed * with RSA, and the signature result is encoded *Base64 * to get the signature value.