# Access Authentication Manager

    /*
    **	(c) COPYRIGHT MIT 1995.
    **	Please first read the full copyright statement in the file COPYRIGH.
    */

The Authentication Manager is a registry for Authentication Schemes that follow the generic syntax defined by the HTTP `WWW-authenticate` and `Authorization` headers. Currently, the only scheme defined is Basic Authentication, but Digest Authentication will soon follow. All Authentication Schemes are registered at run-time in form of an Authentication Module. An Authentication Module consists of the following:

scheme
  The name which is used to identify the scheme. This is equivalent to the `<scheme>` part of the `WWW-authenticate` HTTP header, for example "basic"
BEFORE Filter
  When a new request is issued, the Authentication Manager looks in the URL tree to see if we have any access authentication information for this particular request. The search is based on the realm (if known) in which the request belongs and the URL itself. If a record is found then the Authentication Manager calls the Authentication Module in order to generate the credentials.
AFTER Filter
  After a request has terminated and the result was lack of credentials, the request should normally be repeated with a new set of credentials. The AFTER filter is responsible for extracting the challenge from the HTTP response and store it in the URL tree, so that we next time we request the same URL we know that it is protected and we can ask the user for the appropriate credentials (user name and password, for example).
garbage collection
  The authentication information is stored in a URL Tree but as it doesn't know the format of the scheme specific parts, you must register a garbage collector (gc). The gc is called when node is deleted in the tree.

Note: The Authentication Manager itself consists of BEFORE and an AFTER filter - just like the Authentication Modules. This means that any Authentication Module also can be registered directly as a BEFORE and AFTER filter by the Net Manager. The reason for having the two layer model is that the Authentication Manager maintains a single URL tree for storing access information for all Authentication Schemes.

An Authentication Module has three resources, it can use when creating challenges or credentials:

- Handle the credentials which is a part of the Request obejct. The credentials are often generated by asking the user for a user name ansd a password.
- Handle the challenges which is a part of the Request object. The MIME parser will normally find the credentials as we parse the HTTP response.
- Add information to the URL Tree

This module is implemented by HTAAUtil.c, and it is a part of the W3C Sample Code Library.

    #ifndef HTAAUTIL_H
    #define HTAAUTIL_H
    #include "HTReq.h"
    #include "HTNet.h"
    #include "HTUTree.h"

## Authentication Scheme Registration

An Authentication Scheme is registered by registering an Authentication Module to in the Authentication Manager.

### Add an Authentication Module

You can add an authentication scheme by using the following method. Each of the callback function must have the type as defined below.

    typedef struct _HTAAModule HTAAModule;

    extern HTAAModule * HTAA_newModule (const char *		scheme,
    				    HTNetBefore *		before,
    				    HTNetAfter *		after,
    				    HTNetAfter *                update,
    				    HTUTree_gc *		gc);

### Find an Authentication Module

    extern HTAAModule * HTAA_findModule (const char * scheme);

### Delete an Authentication Module

    extern BOOL HTAA_deleteModule (const char * scheme);

### Delete ALL Authentication modules

    extern BOOL HTAA_deleteAllModules (void);

## Handling the URL Tree

The authentication information is stored as URL Trees. The root of a URL Tree is identified by a hostname and a port number. Each URL Tree contains a set of templates and realms which can be used to predict what information to use in a hierarchical tree.

The URL trees are automatically collected after some time so the application does not have to worry about freeing the trees. When a node in a tree is freed, the gc registered as part of the Authentication Module is called.

Server applications can have different authentication setups for each hostname and port number, they control. For example, a server with interfaces "`www.foo.com`" and "`internal.foo.com`" can have different protection setups for each interface.

### Add new or Update a Note in the UTree

Add an access authentication information node to the database or update an existing one. If the entry is already found then it is replaced with the new one. The template must follow normal URI syntax but can include a wildcard Return YES if added (or replaced), else NO

    extern void * HTAA_updateNode (BOOL proxy,
                                   char const * scheme,
    			       const char * realm, const char * url,
    			       void * context);

### Delete a Node from the UTree

This is called if an already entered node has to be deleted, for example if it is not used (the user cancelled entering a username and password), or for some reason has expired.

    extern BOOL HTAA_deleteNode (BOOL proxy_access, char const * scheme,
                                 const char * realm, const char * url);

## The Authentication Manager Filters

As mentioned, the Access Authentication Manager is itself a set of filters that can be registered by the Net manager.

### Before Filter

Make a lookup in the URL tree to find any context for this node, If no context is found then we assume that we don't know anything about this URL and hence we don't call any BEFORE filters at all.

    HTNetBefore HTAA_beforeFilter;

### After Filter

Call the AFTER filter that knows how to handle this scheme.

    HTNetAfter HTAA_afterFilter;

### Update Filter

Call the UPDATE filter that knows how to handle this scheme.

    HTNetAfter HTAA_updateFilter;

### Proxy Authentication Filter

Just as for normal authentication we have a filter for proxy authentication. The proxy authentication uses exactly the same code as normal authentication but it stores the information in a separate proxy authentication URL tree. That way, we don't get any clashes between a server acting as a proxy and a normal server at the same time on the same port. The difference is that we only have a ingoing filter (a before filter) as the out going filter is identical to the normal authentication filter. The filter requires to be called after a proxy filter as we otherwise don't know whether we are using a proxy or not.

    HTNetBefore HTAA_proxyBeforeFilter;

    #endif	/* NOT HTAAUTIL_H */