about proxy authentication with external program

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I have some questions about above subject.

I am using squid 2.1 patch 2. and using following config

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acl members proxy_auth cliff inking

http_access allow memberss

authenticate_program /.../ncsa_auth /..../passwd

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I am wondering followings

1. when user connect firstly, Is passwd file created automatically ?

2. what 's the purpose of the "TAG: proxy_auth_realm" ?
    ( I am not using this tag now )