1  –  host-variable

    Specifies the name of the user and the password to whom the
    database attach is being transferred as a string literal or a
    host variable. If a host-variable is specified, it must contain
    the literal-user-auth as a string literal.

2  –  USER 'username'

    A character string literal that specifies the operating system
    user name that the database system uses for privilege checking.

3  –  USING 'password'

    A character string literal that specifies the user's password for
    the user name specified in the USER clause.