参考：

https://*.com/questions/19605150/regex-for-password-must-contain-at-least-eight-characters-at-least-one-number-a

实际：

• At least 8 characters long;
• At most 20 characters long;
• One lowercase / one uppercase, one number and one special character;
• No whitespaces.

'^(?=.*[0-9])(?=.*[a-zA-Z])(?=.*[@$!%*?&^#~])([a-zA-Z0-9@$!%*?&^#~]{8,20})$'