oracle authid cursor

How can a CURSOR inside a stored procedure accept variables passed in as a parameter? We want the cursor to SELECT from any schema we have in the database so we would like to pass in a variable for the schema name and have the cursor use this schema_name when it is defined.   For example how can I get something like this to work:

CREATE PROCEDURE TEST (schema_name_parameter IN varchar2)
authid current_user
as

begin
declare
  variable_junk char(1);
  cursor a
  as
     select junk from schema_name_parameter.table_junk;  

  begin
    open a;
    fetch junk into variable_junk;
 end;

end;
end test;
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