masterUserPassword  
  The password for the master user.
Constraints:
- Can't be specified if - ManageMasterUserPasswordis turned on.
- Can include any printable ASCII character except "/", """, or "@". For RDS for Oracle, can't include the "&" (ampersand) or the "'" (single quotes) character. 
Length Constraints:
- RDS for Db2 - Must contain from 8 to 128 characters. 
- RDS for MariaDB - Must contain from 8 to 41 characters. 
- RDS for Microsoft SQL Server - Must contain from 8 to 128 characters. 
- RDS for MySQL - Must contain from 8 to 41 characters. 
- RDS for Oracle - Must contain from 8 to 30 characters. 
- RDS for PostgreSQL - Must contain from 8 to 128 characters.