sp_adduser (Transact-SQL MetaData) Definition

Please note: that the following source code is provided and copyrighted by Microsoft and is for educational purpose only.
The meta data is from an SQL 2012 Server.

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Definition:

sys.sp_adduser(nvarchar @loginame
, nvarchar @name_in_db
, nvarchar @grpname)

MetaData:

 create procedure sys.sp_adduser  
    @loginame       sysname,        --  user's login name in syslogins  
    @name_in_db     sysname = NULL, --  user's name to add to current db  
    @grpname        sysname = NULL  --  role to which user should be added.  
as  
    --  SETUP RUNTIME OPTIONS / DECLARE VARIABLES --   
    set nocount on  
    declare @ret        int  
  
    --  LIMIT TO SQL/NT USERS IN SYSLOGINS (BCKWRD COMPAT ONLY!)  
    if not exists (select * from master.dbo.syslogins where loginname = @loginame  
            and (isntuser = 1 or isntname = 0))  
        and @loginame <> 'guest'  
    begin  
        raiserror(15007,-1,-1,@loginame)  
        return (1)  
    end  
  
    --  VALIDATE THE ROLENAME --   
    if @grpname is not null and  
       not exists (select * from sysusers where name = @grpname and issqlrole = 1)  
    begin  
        raiserror(15014,-1,-1,@grpname)  
        return (1)  
    end  
  
    if @name_in_db is null  
        select @name_in_db = @loginame  
  
    --  In Hydra only the user dbo can do this --   
    if (not is_member('dbo') = 1)  
    begin  
        --  AUDIT FAILED SECURITY CHECK --   
        dbcc auditevent (109, 1, 0, @loginame, @name_in_db, @grpname , NULL, NULL, NULL, NULL)  
        raiserror(15247,-1,-1)  
        return (1)  
    end  
  
    --  ADD THE USER TO THE DATABASE --   
    EXEC @ret = sys.sp_grantdbaccess @loginame, @name_in_db OUT  
    if (@ret <> 0)  
        return (1)  
  
    --  ADD USER TO ROLE IF GIVEN. NOP FOR 'public' --   
    if (@grpname is not null) and (@grpname <> 'public')  
    begin  
        EXEC @ret = sys.sp_addrolemember @grpname, @name_in_db  
        if @ret <> 0  
        begin  
            --  "ROLLBACK" THE ABOVE sp_grantdbaccess --   
            exec sys.sp_revokedbaccess @name_in_db  
            return (1)  
        end  
    end  
  
    --  RETURN SUCCESS --   
    return (0) --  sp_adduser