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The Evolution of Web Applications In the beginning, web applications were just a collection of static HyperText Markup Language (HTML) pages. Earlier versions of HTML allowed web developers to use text, some formatting tags, images, and a few widgets in their pages. The first sites and applications concentrated more on presentation aspects. This quickly became a problem since HTML was created to be a data modeling language and not a true presentation vehicle: it was meant to describe the structure of a document by separating data from metadata (head/body) leaving the browser to render the page. Programmers then added a bit of logic to their applications mainly to do some form processing and user tracking. The first functions were simply bolted to the old view-only applications. Common Gateway Interface (CGI) scripts, usually written in Perl, were the main tools to add logic to a web site. Later on, plenty of new programming alternatives emerged ColdFusion, mod_perl, Python, ASP, JSP, and PHP. Dynamic web applications added more complexity to the logic of a web application, since the scripts have to access, pull, transform, and format the data: Technology Advantages Disadvantages PHP Executed as a web-server Some compatibility issues module, PHP runs really when ported to fast. Lots of extensions non-Apache web servers and ad-hoc functions or platforms mainly greatly reduce regarding specific development time. extensions. CGI programming Allows us to develop It’s an old-fashioned way dynamic pages using a of programming and the very wide range of slowest alternative for the programming languages development of web (Perl, C, Python, Lisp to pages. name a few). mod_perl Runs the Perl interpreter Not portable to other web as an Apache module. servers. Provides the performance of PHP. mod_python Runs Python as an Not portable to other web Apache module. Provides servers. better performance than CGI programming. Java Servlets Very high portability. All The disadvantages of Java the Java features can be are adopted too (slow used. performance, higher development time). FastCGI A modern approach to CGI Not very popular, not very scripting. Increases portable. performance and allows us to program in a wide range of programming languages. ASP Short development time Not portable. Proprietary and acceptable language. performance. As developers thought of ways to store and manage data, they encountered the principle of a content Page 527

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Chapter 15: Introduction to Multi-Tier Development Overview Import ant This is a reminder that all source code and support for this blog can now be found at http://www.apress.com, even though references within the chapters may point to http://www.wrox.com. Multi-tier development is a development process oriented to create software that is easy to maintain and integrate. As the various Apache and C libraries open themselves to PHP programmers, the time to start thinking multi-tier is now. As we move through the chapter we will look at: . The evolution of web applications . The three tier architecture . Generic multi-tier architectures . Goals of multi-tiering . Various models of developing multi-tier applications . HTML-based architecture . XML-based architecture Page 526
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Summary In this chapter, we looked at: . Directory services in general . LDAP as a directory technology . Components that make up a typical LDAP setup . Characteristics and features that make LDAP the directory technology of choice . The four models of LDAP and thereby the underlying mechanisms required for LDAP solutions . The software options currently available for LDAP . Installation and configuration of an open-source solution . The PHP client API for LDAP support . A simple application that illustrated the use of the API Page 525
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employeenumber: 3123283622 telephonenumber: 666-767-2000 userpassword: faginm123 dn: mail=maryx@foowi.com, ou=Marketing, o=Foo Widgets, c=us cn: Mary sn: Xeyed objectclass: top objectclass: person objectclass: organizationalPerson objectclass: inetOrgPerson mail: maryx@foowi.com ou: Marketing employeenumber: 3223453622 telephonenumber: 111-767-2000 userpassword: maryx123 Also, if we use OpenLDAP for running the application, so as to effect access control, we need to add the following lines to slapd.conf and restart slapd: access to attr=userPassword by self write by anonymous auth by * none access to * by self write by dn=”cn=Admin,o=Foo Widgets,c=us” write by * read The first block indicates that any user can modify their own password and can bind anonymously to the server to authenticate against the password stored in the respository. The second block indicates that a given user can modify their attributes and so can the admin user. It also indicates that all users have read only access to all other attributes of all other entities thereby allowing any user to search the directory. For more information on access control in OpenLDAP, see the OpenLDAP administrator’s guide: http://www.openldap.org/doc/admin/. Page 524

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} } else { displayErrMsg(”Connection to LDAP server failed!”); exit; } } } ?> A typical screen prompting the user to enter the attributes would look like the one below: We need to be aware of certain caveats with this application that arise from the fact that this is merely illustrative of the PHP LDAP API and not a fully-fledged production application. As mentioned before the use of HTTP sessions is highly recommended to indicate authentication status. Further users created using the add mechanism do not have a password field and so modification of such entries is not possible through the current mechanism. To get started with the application we could upload a sample set of user information into the directory using the ldapadd utility that comes with most LDAP client software and then work with it. A typical sample would look like: dn: o=Foo Widgets, c=us objectclass: top objectclass: organization o: Foo Widgets dn: ou=Engineering, o=Foo Widgets, c=us objectclass: top objectclass: organizationalUnit ou: Engineering dn: ou=Marketing, o=Foo Widgets, c=us objectclass: top objectclass: organizationalUnit ou: Marketing dn: mail=faginm@foowi.com, ou=Engineering, o=Foo Widgets, c=us cn: Fagin sn: Maddog objectclass: top objectclass: person objectclass: organizationalPerson objectclass: inetOrgPerson mail: faginm@foowi.com ou: Engineering Page 523
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require(”empdir_common.php”); require(”empdir_functions.php”); At least, the name, e-mail, and department information should be entered. If this is not entered, we display an error and re-display the earlier form: if (!$cn || !$mail || !$ou) { generateHTMLHeader(”Please fill in fields: “); displayErrMsg(”Minimally Name, Dept. and E-mail fields are required!!”); generateHTMLForm(0, “empdir_add.php”, “ADD”); } else { We collect the attributes of the new entry to be added in an associative array: $entryToAdd[”cn”] = $cn; $entryToAdd[”sn”] = $sn; $entryToAdd[”mail”] = $mail; $entryToAdd[”employeenumber”] = $employeenumber; $entryToAdd[”ou”] = $ou; $entryToAdd[”telephonenumber”] = $telephonenumber; $entryToAdd[”objectclass”] = “person”; $entryToAdd[”objectclass”] = “organizationalPerson”; $entryToAdd[”objectclass”] = “inetOrgPerson”; Here we construct the DN corresponding to the new entry: $dnString = “mail=” . $mail . “,” . “ou=”. $ou . “,” . $baseDN; This is the root DN we shall bind to, before performing the add operation: $adminRDN = “cn=Admin,” . $baseDN; We connect to the server and bind as an administrator: $linkIdentifier = connectBindServer($adminRDN, $adminpassword); if ($linkIdentifier) { The actual addition is done here: if (ldap_add($linkIdentifier, $dnString, $entryToAdd) == true) { generateHTMLHeader(”The entry was added succesfully”); returnToMain(); } else { displayErrMsg(”Addition to directory failed !!”); closeConnection($linkIdentifier); returnToMain(); exit; Page 522
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$dnString = “mail=” . urldecode($mail) . “,ou=” . urldecode($ou) . “,” . $baseDN; The script prompts the user for the administrator’s password since this is required for deleting entries from the directory: if (!isset($adminpassword)) { generateHTMLHeader(”Administrator action:”); promptPassword($mail, $ou, “empdir_delete.php”); return; } Here the DN of the administrator user is hard-coded. Ideally there can be a whole category of administrative users and the roles and privileges of these users can be managed by using the HTTP sessions in tandem with the LDAP implementation’s authentication and authorization mechanism: $adminRDN = “cn=Admin,” . $baseDN; We connect to the server and bind as the administrator user: $linkIdentifier = connectBindServer($adminRDN, $adminpassword); if ($linkIdentifier) { The actual deletion is performed using the DN string we constructed earlier: if (ldap_delete($linkIdentifier, $dnString) == true) { generateHTMLHeader(”The entry was deleted succesfully”); returnToMain(); } else { displayErrMsg(”Deletion of entry failed !!”); closeConnection($linkIdentifier); exit; } } else { displayErrMsg(”Connection to LDAP server failed!!”); exit; } ?> This script is invoked when the user clicks on the ADD button from the main screen:

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edit these fields and click the MODIFY button: generateHTMLForm($resultEntry, “empdir_modify.php”, “MODIFY”); closeConnection($linkIdentifier); } else { This block gets executed as a result of submitting the afore-mentioned form. The new parameters are gathered into an associative array to be passed to the server: $dnString = “mail=” . $mail . “,” . “ou=”. $ou . “,” . $baseDN; $adminRDN = “cn=Admin,” . $baseDN; $newEntry[”cn”] = $cn; $newEntry[”sn”] = $sn; $newEntry[”employeenumber”] = $employeenumber; $newEntry[”telephonenumber”] = $telephonenumber; We connect to the server and bind as the user who’s DN is to be modified: $linkIdentifier = connectBindServer($dnString, $userpassword); if ($linkIdentifier) { if ((ldap_modify($linkIdentifier, $dnString, $newEntry)) == false) { displayErrMsg(”LDAP directory modification failed !!”); closeConnection($linkIdentifier); exit; } else { generateHTMLHeader(”The entry was modified succesfully”); returnToMain(); } } else { displayErrMsg(”Connection to LDAP server failed”); exit; } } ?> This is an example of a typical modification screen: This function is invoked when the user clicks the Delete link in the Edit column of the search results: Note: If you are looking for good and quality webspace to host and run your java application check professional java hosting services

$searchFilter); if ($resultEntries) { generateHTMLHeader(”Search Results:”); printResults($resultEntries); returnToMain(); } else { returnToMain(); } } else { displayErrMsg(”Connection to LDAP server failed !!”); closeConnection($linkIdentifier); exit; } } } ?> This is a sample screen of search results: This script is called when a user clicks on the Modify link in the Edit column of a search result:

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($formValues) ? $formValues[0][”employeenumber”][0] : “”); printf(”Department:  
n”, ($formValues) ? $formValues[0][”ou”][0] : “”); printf(”Telephone:   
n”, ($formValues) ? $formValues[0][”telephonenumber”][0] : “”); If this function is called from the modification script, it outputs an extra text field for the password of the user modifying the entry corresponding to them: if ($submitLabel == “MODIFY”) { printf(”User Password:    
n”); } If the function is called from the script responsible for adding users, it outputs a text field to prompt the user for the administrator’s password: if ($submitLabel == “ADD”) { printf(”Admin Password:    
n”); } printf(”“, $submitLabel); printf(”

“); } This function merely provides a link to the main page: function returnToMain() { printf(”