If you want to use mod_auth_external.c with a hardcoded internal function,
then you first have to hardcode an internal function (who wudda thunk?).
Here are Tyler Addison's instructions for this:
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Step 1:
	Edit "mod_auth_external.c"

Step 2:
	Uncomment the _HARDCODE_ #define.
	Uncomment the line:
              /* #include "your_function_here.c" */

Step 3:
	Replace "your_function_here.c" with the path/name of your function.

Step 4:
	Choose a <function name> for your function. ie: 'RADIUS' or 'SYBASE'
	This will be used for telling mod_auth_external which hard coded
	function you want to call.

Step 5:
	Go down to the large commented section in the middle of the
	"mod_auth_external.c" and follow the instructions there.

	Your function should start something like:


	int
	function_name (char *user_name,char *user_passwd,char *config_path) {


	The function call in mod_auth_external.c should look something like:


        if (strcmp(check_type,"<type>")==0) {
            code = function_name(c->user,sent_pw,config_file);
        }

	** BIG NOTE TO PROGRAMMERS **
	-DO NOT- use exit() or other such calls that will cause your
	function to exit abnormally or dump core. It will take the entire 
	httpd with it and display a message to your browser saying "no data". 
	Use return() instead of exit().

Step 6:
	Save your work

Step 7:
	In the Apache source tree type:     make
	You should then see make attempt to recompile mod_auth_external.c and
	your function code.

	** If you do not get a clean compile debug your code, and the
	modifications you made to mod_auth_external.c, and try Step 7 again.
	Continue until you get a clean compile.

	** NOTE **
	If you do not make any changes to mod_auth_external.c, but DO make
	changes to your function code, you will need to at least 'touch'
	mod_auth_external.c so 'make' knows you have modified the code.

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Continue by following the configuration instructions in the INSTALL file.