Authentication -- Write your own Filter
written and ©1998, 99 by Kevin Flick www.flicks.com creator of Authentix

Writing your own Basic Authentication filter is an option if you have the skills, resources and time to do it.

Writing your own Basic Authentication filter is the way to go if

• you have special requirements, and commissioning a custom enhancement to a third party Basic Authentication filter is not an option.
• you have the skills, resources and time.
• you want to validate against a specific or proprietary type of datasource, such as flat-file, or your own database.

You won't want to write your own Basic Authentication filter if

• you have a short deadline
• you do not have the skills or resources required
• Basic Authentication is not secure enough for your purposes
• you want all accounts of every type in one userbase, specifically the NT user account database, for administrative reasons.

• a third party tool like AuthentiX meets all your needs

Definitions

• ISAPI = Internet Server Application Programming Interface

How to write your own Basic Authentication filter

You will need to build a dll that conforms to the ISAPI filter specification and has the following entry points:

• GetFilterVersion
• HttpFilterProc

The GetFilterVersion function is the first entry point called by the Internet Information Server. In this function you set the IIS notifications that you want to receive, and any other first time setup tasks.

The HttpFilterProc function is called in response to the notifications set in GetFilterVersion and is where the work of the filter is actually done.

There are several excellent references to help develop an ISAPI filter. Recommended is Que's "Special Edition Using ISAPI", ISBN 0-7897-0913-9 (to which this writer also contributed).

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