SQL> conn raghav/raghav
Connected.
SQL> alter user scott identified by tejajun20;
alter user scott identified by tejajun20
                               *
ERROR at line 1:
ORA-01031: insufficient privileges


SQL> conn system/tejajun20
Connected.
SQL> grant alter user to raghav;

Grant succeeded.

SQL> conn raghav/raghav
Connected.
SQL> alter user scott identified by tejajun20;
alter user scott identified by tejajun20
*
ERROR at line 1:
ORA-28007: the password cannot be reused


SQL> alter user scott identified by teja;

User altered.

SQL> sho user
USER is "RAGHAV"
SQL>

create or replace procedure change_password (
  p_username in varchar2,
  p_password in varchar2
)
is 
begin
  -- Check parameters
  if   p_username is null or p_password is null 
    or length(p_username) > 30 or length(p_password) < 8 -- minimum password length
    or upper(p_username) in ('SYS','SYSTEM') -- and so on, or check if username is in a list
  then 
    raise_application_error (-20000, 'Wrong parameter');
  end if;
  execute immediate 
    'alter user '||dbms_assert.schema_name(p_username)||
    ' identified by "'||p_password||'"';
end;
/

SQL> conn raghav/raghav
Connected.
SQL> create or replace procedure change_password (
  2    p_username in varchar2,
  3    p_password in varchar2
  4  )
  5  is
  6  begin
  7    -- Check parameters
  8    if   p_username is null or p_password is null
  9      or length(p_username) > 30 or length(p_password) < 8 -- minimum password length
 10      or upper(p_username) in ('SYS','SYSTEM') -- and so on, or check if username is in a list
 11    then
 12      raise_application_error (-20000, 'Wrong parameter');
 13    end if;
 14    execute immediate
 15      'alter user '||dbms_assert.schema_name(p_username)||
 16      ' identified by "'||p_password||'"';
 17  end;
 18  /

Procedure created.

SQL> conn system/bhanu
Connected.
SQL> create user ashish identified by bhanu account unlock;

User created.

SQL> grant create session to ashish;

Grant succeeded.

SQL> grant execute on change_password to ashish;
grant execute on change_password to ashish
                 *
ERROR at line 1:
ORA-04042: procedure, function, package, or package body does not exist


SQL> grant execute on raghav.change_password to ashish;

Grant succeeded.

SQL> sho user
USER is "SYSTEM"
SQL> conn ashish/bhnau
ERROR:
ORA-01017: invalid username/password; logon denied


Warning: You are no longer connected to ORACLE.
SQL> conn ashish/bhanu
Connected.
SQL> set serveroutput on
SQL> exec change_password('SCOTT','ASHISH');
BEGIN change_password('SCOTT','ASHISH'); END;

      *
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00201: identifier 'CHANGE_PASSWORD' must be declared
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored


SQL> exec raghav.change_password('SCOTT','ASHISH');
BEGIN raghav.change_password('SCOTT','ASHISH'); END;

*
ERROR at line 1:
ORA-20000: Wrong parameter
ORA-06512: at "RAGHAV.CHANGE_PASSWORD", line 12
ORA-06512: at line 1


SQL> exec raghav.change_password('SCOTT','oracleoca');

PL/SQL procedure successfully completed.

SQL> conn scott/oracleoca
Connected.
SQL> alter user system identified by oracleoca;

User altered.

SQL> conn system/oracleoca
Connected.
SQL>