add cookie in handler process

[whut_jia]

Hello,
I am new to apache module development,and now I have a problem.
Now,I am writing a handler module.In this module,I need validate 
username/password infomation sent by user.After validating,I set cookie into 
headers_out(apr_table_set(r->headers_out,"Ser-Cookie","....")),and then do 
external redirection (apr_table_setn(r->headers_out,"Location"," URL")).The 
question is that I just get Location header but get Cookie header when I access 
to apache server.why??
Many thanks,
Jia