The pathway to a simple login system

AuthenticationSys.c

// Find User _AND_ Return User Information
// -----------------------------------
// Documentation:
//  This function will scan the Primary Linked-List for the user's account.
//  If an account exists, then we will provide the user's card and provide
//  a successful status.  But, if the account does not exist or the credentials
//  are incorrect, the user's card is NULL with a failure status.
// -----------------------------------
// Parameters:
//  cList [CustomerData]
//      The Primary Linked-List to reference from.
//  userCard [CustomerData]
//      The User's Account Information; if exists in Database, return the
//      user's information for general program use.
//  userID [char*]
//      User's Screen Name (or  Login ID) to access the store via user account.
//  UserKey [char*]
//      User's Password to access their account.
// -----------------------------------
// Output:
//  True ( 0 < x)
//      Credentials matched against the Database.
//      Found user's account
//      User's Card has been initialized
//  False ( 0 )
//      Credentials didn't match against the Database.
//      OR Failure to find the user's account.
//      User's Card remains NULL.
// -----------------------------------
bool FindUser_ReturnUserInfo(CustomerData *cList,
                            CustomerData **userCard,
                            char *userID,
                            char *userKey)
{ 
    // Traverse through the Linked-List until we find the user's ID or reach NULL.
    while (cList != NULL && (0 != strcmp(cList->userID, userID)))
        cList = cList->next;
        
    // Once we leave the loop, determine what happened.
    //  Because we left the loop, we don't know if we found the user's account
    //  or if we reached NULL within the Linked-List.
    if (cList == NULL)
    {
        // Reached end of the Linked List, user's account was not found.
        userCard = NULL;        // If incase it was not done so previously, NULL the card now.
        return false;           // Return a failure signal.
    } // if :: NULL
    else if (0 == strcmp(cList->userID, userID))
    {   // Found the User's ID!
        // Check if the user's password challenge matches
        if (0 == strcmp(cList->userKey, userKey))
        {
            userCard = &cList;
            return true;
        } // if :: Successful!
        
        // Else, the password was incorrect.
        userCard = NULL;        // If incase it was not done so previously, NULL the card now.
        return false;           // Return a failure signal.
    } // if :: Found User Account!
    else
    {
        // Something went horribly wrong; if we reach here - throw a hard-crash.
        printf("    <!> CRITICAL FAILURE <!>\n");
        printf("------------------------------------\n");
        printf("Unable to successfully obtain account details.  Some reasons for this nasty message:\n");
        printf(" *Linked-List was corrupted\n");
        printf(" *Improper Conditional Checks\n");
        printf(" *Or worse, a very unknown error\n");
        printf("Please send your complaints to the slave monkey coders.  We don't pay them anything, so please be some-what nice to them!\n");
        
        // Send a hard-crash-out.
        exit(1);
    } // Something went horribly wrong....
} // FindUser_ReturnUserInfo()