WebDAV: What It Is, What It Does, Why You Need It
`
`Luis O. Hernández
`Institutional Technology
`Ringling School of Art & Design
`Sarasota, FL 34234
`941-359-7633
`lhernand@ringling.edu
`
`Mahmoud Pegah
`Institutional Technology
`Ringling School of Art & Design
`Sarasota, FL 34234
`941-359-7633
`mpegah@ringling.edu
`
`ABSTRACT
`Legacy network file services such as NFS, SMB/CIFS, and AFP
`changed the way we worked. File services running on cross-
`platform networks allowed us to save our files on remote systems
`and changed the way we exchanged files with each other. Web
`technology changed our lives and the way we work again. In the
`fall of 2002, due to the demand for a web integrated network file
`service with powerful content management capabilities, we are
`offering WebDAV (Web-based Distributed Authoring and
`Versioning) service in our instructional computer laboratories at
`Ringling School of Art and Design. WebDAV is a set of
`extensions to HTTP (the protocol that drives the web), which
`allows users to collaborate with each other to edit and manage
`files on web servers across the network.
`
`WebDAV allows our institution to host a shared file space for
`each course. Students in a course can access the shared space for
`collaboration with the instructor and other students in the same
`course. Access
`to
`the WebDAV share
`is seamless by
`incorporating LDAP (Lightweight Directory Access Protocol) into
`the system to maintain single sign-on.
`
`In our implementation, we have integrated the Apache web server,
`Apache extensions for WebDAV and the LDAP based meta-
`directory model for user authentication information. Furthermore,
`we have implemented a Perl script, which runs every hour to
`monitor WebDAV storage usage and triggers alarms for any disk
`quota breach.
`
`In this technical report, we will share our framework, tips and
`tricks we learned from our deployment of WebDAV with our
`colleagues. We will explain how legacy network file services can
`be strengthened by providing WebDAV service on both the
`Windows and Unix platforms. Furthermore, we will discuss the
`issues we had to address and the lessons we learned during and
`after the deployment process.
`
`Categories and Subject Descriptors
`D.4.3 [Operating Systems]: File Systems Management – access
`methods, distributed file systems, file organization.
`
`
`Permission to make digital or hard copies of all or part of this work for
`personal or classroom use is granted without fee provided that copies are
`not made or distributed for profit or commercial advantage and that
`copies bear this notice and the full citation on the first page. To copy
`otherwise, or republish, to post on servers or to redistribute to lists,
`requires prior specific permission and/or a fee.
`SIGUCCS’03, September 21–24, 2003, San Antonio, Texas, USA.
`Copyright 2003 ACM 1-58113-665-X/03/0009…$5.00.
`
`
`General Terms
`Documentation, Performance, Design, Reliability, Security
`
`Keywords
`Apache, Authoring, File Service, File Sharing, HTTP, Internet,
`LDAP, Server, Quota, Versioning, Web, WebDAV
`
`1. INTRODUCTION
`WebDAV (Web Distributed Authoring and Versioning) allows for
`file management through a web server by extending the HTTP
`protocol. WebDAV is documented in RFC 2518 and extended in
`RFC 3253. RFC 2518 specifies a set of methods, headers, and
`content-types ancillary to HTTP/1.1 for the management of
`resource properties, creation and management of resource
`collections, namespace manipulation, and resource
`locking
`(collision avoidance) [20]. RFC 3253 specifies a set of methods,
`headers, and resource types that define the WebDAV versioning
`extensions to the HTTP/1.1 protocol [21]. For common users,
`WebDAV allows web development teams and other workgroups
`to use a remote web server as easily as if it were a local file server
`[2].
`Software vendors have adopted WebDAV with minor deviations
`from the RFCs, such as authoring extensions and versioning.
`These deviations from the RFCs are not critical for clients to
`access files from a server. Mac OS X, Apple’s latest operating
`system, offers WebDAV support to the desktop level. Microsoft
`Windows has supported WebDAV since Windows 2000 and
`Office 2000 [9].
`Since WebDAV support to the desktop level is available for two
`of the most popular operating systems, institutions can offer
`WebDAV shares instead of the compute-intensive SMB shares, or
`the incompatible AFP or NFS shares. For instance, every
`connection to a Samba share requires a separate running process
`that does not expire until the share is closed. If an institution
`already uses a web server such as the Apache web server, the
`institution can easily lower the use of Samba shares and free the
`load on the servers for other uses.
`Apple’s AFP has been available since 1984. Although the
`protocol has improved over time, support for the aging protocol is
`thinning in favor of NFS as of Mac OS X. Although NFS is the de
`facto standard for sharing files across multiplatform systems,
`Windows support is non-existent without elaborate and expensive
`support from third-party vendors. WebDAV offers a solution
`compatible with both systems that is easy to use and inexpensive
`to implement.
`
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`

`

`In this report, we will explain our approach to using WebDAV on
`our campus, installation, configuration, the lessons we learned
`from our framework installation, alternative clients available for
`WebDAV support in operating systems other than Windows and
`Mac OS X, and suggestions that would make WebDAV easier to
`administer and use.
`
`2. DISTRIBUTIONS, INSTALLATION,
`AND CONFIGURATION
`Enabling WebDAV support in the Apache web server is a
`straightforward process. A web server administrator needs to find
`the package distributions, compile the module into the Apache
`web server, and then add a few lines to the Apache configuration
`file to enable web shares in specific folders.
`2.1 Distributions Used
`An Apache module for WebDAV support within the Apache web
`server has been available since 2000 [15]. Since then, the
`WebDAV module has been updated regularly to include new
`functionality and support for later Apache distributions.
`To maintain single sign-on, another module can be included
`during compilation. The LDAP Authorization Module has been
`available for the Apache web server since 1998 [11]. The module
`allows administrators to bypass htpasswd generated files for
`authentication within Apache and instead use an LDAP server to
`authenticate users with their existing accounts. A simple change
`within the standard WebDAV configuration in the Apache
`configuration file allows user authentication to WebDAV shares
`against an LDAP server. The installation and configuration that
`follows refers to the following distributions: Apache web server
`version 1.3.27, WebDAV module version 1.3.6, and LDAP
`module version 2.3.
`
`2.2 Installation
`Experienced Apache administrators will find the WebDAV and
`LDAP module installations straightforward [11][14][19]. During
`the configuration of
`the Apache source distribution,
`the
`administrator must specify that both the WebDAV and LDAP
`module should be marked for inclusion during compilation of the
`package:
`
`# Apache web server configure command
`./configure \
`--prefix=/local/apache_1.3.27 \
`--enable-module=proxy \
`--activate-module=src/modules/dav/libdav.a \
`--activate-
`module=src/modules/ldap/mod_auth_ldap.c
`Library modules should be compiled statically to improve
`performance during execution time and startup time [5], and to
`allow for binary portability across other systems with the same
`operating system as where the package is originally compiled.
`Another advantage of static compilation is that the Apache web
`server software is generally upgraded more often than the Apache
`modules. The ease of administration that Apache’s Dynamically
`Shared Objects
`(DSO) provides diminishes when
`the
`administrator must install a newer version that includes security
`enhancements as DSO modules must be recompiled.
`
`2.3 Configuration
`Once the WebDAV and LDAP modules are compiled into the
`Apache web server, the web server configuration does not require
`any changes until WebDAV functionality is required. The
`WebDAV module can be enabled in the Apache configuration as
`follows [14]:
`# Enable WebDAV support
`Addmodule mod_dav.c
`DAVLockDB /local/apache/var/DAVLock
`To enable standard WebDAV support within specific web folders
`using htpasswd generated files, the administrator must include
`several WebDAV configuration parameters
`in
`the Apache
`configuration within the web folder chosen for WebDAV support.
`The configuration consists of activating WebDAV support for the
`specific folder, and limiting access to the following requests using
`the “Limit” directive: PUT, POST, DELETE, PROPFIND,
`PROPPATCH, MKCOL, COPY, MOVE, LOCK, and UNLOCK.
`Browsing should be disabled for WebDAV enabled folders that
`should not be accessible over the web. To do so, the attribute
`“GET” and “POST” should be added to the “Limit” directive. The
`tool htpasswd (created during the Apache web server compilation
`and generally located in the apache/bin folder) is used to store
`user accounts and passwords to a file. For security purposes, the
`password file must be saved to a folder not included in the web
`server’s DocumentRoot; otherwise, the file will be accessible from
`the
`Internet. The
`file
`is
`referenced with
`the directive
`“AuthUserFile.” The attribute “require user [username]” within
`the “Limit” directive allows the administrator to specify which
`users in the “AuthUserFile” have access to the web share.
`A simple WebDAV setup consists of a web server and the clients
`that connect to the service as shown in Figure 1. The following is
`an example of a standard WebDAV configuration section within
`the Apache configuration file:
`# WebDAV folder for a Project
`<Directory “[DocumentRoot]/project”>
`
`DAV On
`#
`RSADShareDAVOwnerUID [owneruid]
`#
`RSADShareDAVSize [Quota in MB]
`
`AllowOverride None
`
`AuthName “[Project Title]”
`
`AuthType Basic
`
`AuthUserFile [/.hiddenFolder/.hiddenFile]
`
`<Limit [PUT DELETE PROPFIND
`PROPPATCH MKCOL COPY MOVE LOCK
`UNLOCK]>
`
`
`
`
`
`
`
`
`
`</Limit>
`</Directory>
`
`Require user [user names]
`Order Deny,Allow
`Deny from all
`Allow from trusteddomain.com
`
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`

`

`and
`“RSADShareDAVOwnerUID”
`attributes
`The
`“RSADShareDAVSize” are not standard Apache or WebDAV
`configuration attributes. A monitoring tool described later in the
`report uses the attributes to monitor the share disk usage. As you
`can see, they are commented out so the web server does not use
`them.
`
`2.4 Other Distributions
`WebDAV support is available on several distributions other than
`for the Apache web server. Available alternatives exist as servers,
`clients, and as plug-ins.
`2.4.1 Servers
`Several other web servers besides the Apache web server are
`available with embedded WebDAV support in varying forms.
`Microsoft’s Internet Information Server [10] and Mac OS X
`Server [3] support WebDAV out of the box. Although both
`platforms have added functionality in their implementations that
`are not compatible outside of their environment, any WebDAV
`client is able to connect to the servers without the need to use the
`added functionality of the individual implementation.
`Another server on the open source arena is the Neon web server,
`which is in development stages (release 0.23.9). Neon is an HTTP
`and WebDAV client library, with a C interface which features
`integrated WebDAV support [12].
`2.4.2 Clients
`WebDAV support is embedded in the latest version of Microsoft
`Windows, Mac OS X, and GNOME Nautilus and KDE for Linux.
`Client alternatives exist for other systems: Goliath for Mac OS 9
`and Java DAV Explorer for the JVM. A command-line interface is
`also available for use in UNIX terminals, called Cadaver [15].
`2.4.3 Additional Distributions
`Some application programs use plug-ins to enable WebDAV
`capabilities. Such plug-ins includes: jEdit WebDAV plugin for
`the Jedit text-editing application [16] and Eldav for Emacs [18].
`Application programming interfaces (API) are also available for
`popular programming languages: PerlDAV [4] and PythonDAV
`[13].
`A Linux file system driver, DAVfs, is available and allows
`mounts of web folders as a disk drive [17].
`
`3. How to Connect to a Web Share
`The process to connect to a web share depends on the operating
`system or the client used. Here are the steps required to connect
`from Windows or Mac OS X.
`
`3.1 Connecting from Windows
`The following steps allow a user to connect to web folders from a
`Windows machine:
`• Open Internet Explorer and click on File->Open...
`•
`Enter the full URL of the web share. For example,
`http://www.domain.com/WebShare.
`
`
`Figure 1. Simple WebDAV Configuration.
`Administrators can maintain single sign-on by compiling the
`LDAP module with the web server. LDAP authentication to the
`WebDAV
`shares
`is made possible by
`removing
`the
`“AuthUserFile” directive and adding the following directives:
`LDAP_Server, LDAP_Port, Base_DN, and UID_Attr [1]. The
`“require user [username]” attribute can still be used to limit
`authentication to specific usernames; however, LDAP allows
`authentication based on username, group membership, or any
`other attribute found in the directory service.
`A WebDAV setup with LDAP authentication consists of a web
`server, an LDAP server, and the clients that connect to the
`WebDAV service as shown in Figure 2. The configuration is
`similar to a basic WebDAV configuration. The following is an
`example of a WebDAV configuration with LDAP authentication
`enabled within the Apache configuration file:
`# WebDAV folder for a Project
`<Directory “[DocumentRoot]/project”>
`
`DAV On
`#
`RSADShareDAVOwnerUID [owneruid]
`#
`RSADShareDAVSize [Quota in MB]
`
`AllowOverride None
`
`AuthName “[Project Title]”
`
`AuthType Basic
`
`<Limit [PUT DELETE PROPFIND
`PROPPATCH MKCOL COPY MOVE LOCK
`UNLOCK]>
`
`
`
`
`
`
`
`
`
`</Limit>
`
`LDAP_Server ldap.yourdomain.com
`
`LDAP_Port 389
`
`Base_DN “[BaseDN]”
`
`UID_Attr uid
`</Directory>
`
`Require user [user names]
`Order Deny,Allow
`Deny from all
`Allow from trusteddomain.com
`
`
`Figure 2. WebDAV and LDAP Configuration.
`It is important to note that one user owns Apache web server
`processes. The same user must also own all web shares to which
`users will write files; otherwise, the web shares will exist as read-
`only.
`
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`

`usage. After comparing the allotted space and the disk usage, it
`informs the system administrator of any quota breaches, the owner
`of any delinquent share, and the allotted space for the share. The
`script can be web-enabled and can output the results of all shares
`to a web page for use by any IT staff member that requires access
`to the information.
`The load of the WebDAV enabled web server is negligible since
`the added load of the web shares is similar to that of an NFS file
`system. Webalizer is a tool used for web server statistical data that
`creates snapshots of daily usage in web servers. Last semester we
`offered twenty-three WebDAV shares, several of which were used
`simultaneously by classes of more
`than
`twenty students.
`Webalizer reported that web server hits and visits barely increased
`while WebDAV shares were in use.
`5. SECURITY
`As with any web service, WebDAV comes with its share of
`security concerns, specifically authentication and web based
`attacks [22].
`5.1 Authentication
`Basic authentication sends the user’s password in clear text format
`across the network, allowing the possibility of sniffers to steal
`passwords. WebDAV shares can be limited to accept incoming
`connections that generate from specific domains, allowing an
`institution to use basic authentication since the allowed domains
`should be trusted. Other solutions available for authentication
`include shared keys and encrypted connections.
`5.2 Denial of Service
`Web shares are prone to Denial of Service (DoS) attacks. Given
`the possibility of multiple users flooding the server with large
`files, the server would not be able to respond to other requests
`until the large files are processed. More server memory and an
`increase in the number of allowed Apache web server processes
`would diminish the probability of DoS attacks. The increase in
`number of allowed web server processes can be accomplished
`through the web server configuration file.
`5.3 Module Signature
`An attacker is able to determine exactly what a web server is
`running by visiting http://www.netcraft.net. The WebDAV
`module is identified as an addition to the web server. Unless the
`attacker is aware of the exact location of the web share, or unless
`anonymous shares exist, an attacker cannot compromise the
`system if proper authentication mechanisms are in place.
`
`6. LESSONS LEARNED
`We have learned how to work around issues inherent to the
`WebDAV module implementation: mainly no quota system, a
`single authoritative user, and how to replicate the installation in
`other systems. In the following sections are some suggestions on
`how to make the system stronger and more usable through
`modifications to the module and through third-party tools.
`6.1 No Quota System
`tools are
`As explained previously, customized monitoring
`necessary to monitor disk usage of the shares or users can abuse
`disk space limits. In our experience, technology savvy users
`generally do not abuse disk space. During setup, we ask the
`
`
`
`• Check the box on “Open as Web Folder” and click
`“Ok.”
`3.2 Connecting from Mac OS X
`The following steps allow a user to connect to web folders from
`Mac OS X.
`• Within the Finder, click on Go->Connect to Server... or
`press “Command Key + K.”
`Enter the full URL of the web share. For example,
`http://www.domain.com/WebShare.
`
`•
`
`•
`The “Connect” button will trigger a login screen.
`• Upon successful login, a mounted drive will appear on
`the desktop. For security purposes, the drive should be
`unmounted when no longer in use.
`
`
`
`
`When users connect to the web shares, they need to log in using
`their username and password. Upon successful authentication, the
`user is able to view the web folder as any other folder in the
`computer.
`
`4. MONITORING TOOLS
`Since the Apache web server should not run as root due to
`security concerns, the web server will not be able to sudo and act
`on behalf of other users. The user that owns the web server
`process must also own all WebDAV enabled folders and files
`within. This creates a situation in which users can write to a file
`system without a quota, allowing the file system to become full.
`Perl scripts can monitor the usage of each WebDAV enabled
`folder in a system [7]. A cronjob can be set every hour to activate
`the Perl script. The script scans the Apache configuration file for
`each WebDAV share, for attributes that reveal the owner of each
`share, and for the space allotted to each share. The Perl script then
`calls the UNIX command du on each share to determine disk
`
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`

`faculty member how much space is required for the share and
`generally, the class stays within limits. We have only experienced
`few instances when we must call upon the faculty member to
`clean up the share to conserve space. Faculty members have been
`helpful and cooperative in the cleanup process and in following
`up with students who use the most space.
`When we create a web share, we also create a folder for each user
`of the share to place his/her work. Separate student folders allow
`the faculty and IT to monitor disk space usage more efficiently.
`6.2 Single Authoritative User
`Even though users can overwrite each other’s work since one user
`owns the web server processes, students have been respectful of
`each other’s work while working in the shared space. Regardless,
`limiting the web server to run as only one user also limits the
`capability and potential applications that can be created with the
`web server. For example, if the web server were allowed to
`change running user identification, the web shares would not need
`to be owned by one user and disk quotas could potentially be
`applied to all users or groups who need access to the share.
`Another advantage of allowing the web server to change running
`user identification would be that users would not be able to
`overwrite each other’s files.
`It is unfortunate that root should not own the Apache web server
`process due to security concerns. Until such security issues are
`cleared, the Apache WebDAV module will be limited to read and
`write files as one user.
`6.3 Replication
`Our implementation of WebDAV was accomplished with the
`Apache web server version 1.3.27, the WebDAV module version
`1.3.6, and LDAP module version 2.3 on a Sun Fire 280R machine
`using the Solaris 8 operating system.
`Installation and basic configuration information is available at
`http://www.rsad.edu/~lhernand/webdav and also
`through
`the
`WebDAV community [16]. Experienced administrators should
`compile and configure web servers used
`in production
`environments. A simple oversight can render a server open to
`security breaches and intermittent service.
`6.4 Helpful Suggestions
`The WebDAV module is an addition to the Apache web server;
`hence, it lacks functionality that would make the system stronger
`and more usable. Here is a short list of suggestions that would
`make a WebDAV enabled Apache web server easier
`to
`administer:
`• Allow quotas for individual folders regardless of ownership
`as opposed to user-based or group-based quotas (i.e.
`“quota.directory”.) The addition would require an extension
`to the file systems quota service. Some software vendors
`already feature directory quotas with their file services while
`no open source solution is currently available.
`Implement new attributes in the WebDAV module to alert
`administrators or users of quota breaches in web shares. (i.e.
`DAVDiskLimit, DAVOwner, DAVAlertOn) Alerts could be
`accomplished by a brute-force method using the command-
`line application du or in a more elegant manner with a folder-
`based quota file system. Upon authentication to the web
`share, the module calls a check on either the quota or the
`
`•
`
`disk usage and sends an alert to DAVOwner when the user
`reaches
`the boundary DAVAlertOn
`in
`relation
`to
`DavDiskLimit.
`• Allow the WebDAV module to change the ownership of the
`running process so that it can act on behalf of authenticated
`users and not the process owner of the web server. This
`change would take care of both recommendations above
`since users would not be able to write to the web shares once
`they reach the user-based quota limit. We still do not want to
`run web server processes as root, however. The Internet
`Draft, Quota and Size Properties for DAV Collections,
`explains properties and minor behaviors needed for clients to
`interoperate with quota implementations on web folders [8].
`The draft describes how the client should provide common
`language warning about the status of the user’s quota.
`The latter recommendation involves changes to the module and
`the Apache web server only. The second recommendation can be
`implemented into the module; however, it is only a temporary fix
`to the problem. The second solution would create more processing
`and disk
`input/output
`load on
`the
`server. The
`first
`recommendation would involve changes to the file systems quota
`service, which is not as gracious.
`Interestingly enough, while two of the most popular desktop
`operating systems support WebDAV out of the box, providers of
`Network Appliance Servers (NAS, self-contained storage systems)
`offer their appliances with support for the following protocols:
`CIFS, NFS, HTTP, FTP, NDMP. Even though HTTP is
`supported, WebDAV is not. In conversations with one of the
`providers, they have expressed interest in WebDAV technology.
`Administration and use of NAS with WebDAV support would
`improve with a WebDAV “broker” as shown in Figure 3.
`
`
`Figure 3. WebDAV Broker with WebDAV Enabled NAS.
`The configuration above would require changes in both the
`WebDAV client and server implementations. The idea would be
`that a user would only need to remember one URL to access all of
`his/her shares. For example, a user would connect to a URL that
`points to the WebDAV broker, at that point the user authenticates
`to the broker against LDAP. Once the user authenticates
`successfully, the broker queries the NAS appliances to obtain a
`list of the shares available to the user and sends the list to the
`WebDAV client. Once the user obtains the list of WebDAV
`shares available to him/her, the client would connect directly to
`the NAS appliance as shown in Figure 4, which would consider
`the client authenticated by checking with the WebDAV broker. In
`
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`

`essence, the WebDAV broker would also act as an authentication
`point for the NAS appliances.
`The use of LDAP also opens the possibility to store information
`about the shares in the directory server itself. However, LDAP
`should not serve as a broker since it should not be used to store
`the state of authenticated users due to issues related with security.
`
`
`Figure 4. Clients connect to NAS after authentication.
`
`7. ANNOUNCING A NEW SERVICE!
`Our initial release of web shares took place during fall of 2002.
`We released the service with a minimal amount of users until we
`felt comfortable and understood the issues inherent to WebDAV
`shares. It was then that we realized the need for a quota
`monitoring system and implemented it. Since then, we have
`successfully used web shares for class sharing and for project
`sharing among staff members and administrative units.
`Most faculty members learn of web share availability during their
`introduction to IT upon employment. We have also produced
`online tutorials and electronic communications announcing the
`availability of web shares. Students have also been helpful in
`spreading the word. Once students learn how to use web shares in
`one class, they inform the next faculty member about the features
`and advantages. Faculty members contact IT to request web shares
`for their classes.
`8. ACKNOWLEDGEMENTS
`The authors would like to thank all students, faculty, and staff
`members that have used web shares at our institution and have
`helped by offering feedback as to what helps them work more
`efficiently. Without their support and patience, web shares at our
`institution would be nonexistent. Thanks to our colleagues for
`their support and valuable input. We would also like to thank
`Apple Computer for their generosity, adherence to standards, and
`valuable documentation. Thanks to Sean Conkin and Kris Pegah
`for their constant support and understanding.
`
`9. REFERENCES
`[1] Ali, S., Configuring and Setting up the WebDAV services,
`http://www.tldp.org/HOWTO/Apache-WebDAV-LDAP-
`HOWTO/config-webdav.html#AEN305, 2002
`[2] Apple Computer, What is WebDAV?,
`http://www.apple.com/creative/webpro/technology/webdav/,
`2003
`
`[3] Apple Computer, Setting Up WebDAV for Mac OS X Server,
`http://www.apple.com/creative/webpro/technology/webdavse
`tup/, 2003
`[4] Collins, P., PerlDAV -- A WebDAV client library for Perl5,
`http://www.webdav.org/perldav/, 2003
`[5] Engelschall, R. S., Apache 1.3 Dynamic Shared Object
`(DSO) Support, http://httpd.apache.org/docs/dso.html, 1998
`[6] Glaubiger and Clark, WebDAV: A Plugin for jEdit,
`http://www.webdav.us/home.jsp, 2003
`[7] Hernández, L. O., WebDAV Service Information,
`http://www.rsad.edu/~lhernand/webdav, 2003
`[8] Xythos, B. K., L. D. Xythos and C. W. Netezza, Quota and
`Size Properties for DAV Collections,
`http://www.ietf.org/internet-drafts/draft-ietf-webdav-quota-
`01.txt, 2003 (Draft was available at the time of writing and
`expires on September 2003.)
`[9] Microsoft Corporation, Microsoft Continues to Embrace
`Open Standards by Supporting HTTP Extensions That Will
`Enable the Reading and Writing of Web Documents,
`http://www.microsoft.com/presspass/press/1998/oct98/webda
`vpr.asp, 1998
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`[12] Orton, J., Neon, http://www.webdav.org/neon/, 2003
`[13] Rossum, G. v., DAV client library,
`http://www.lyra.org/greg/python/davlib.py, 2003
`[14] Stein, G., mod_dav Installation and Configuration,
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`[15] Stein, G., mod_dav: a DAV module for Apache,
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`[16] Stein, G., WebDAV Resources, http://www.webdav.org, 2002
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`[18] Teranishi, Y., Eldav: Yet another WebDAV interface for
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`[20] The Internet Society, HTTP Extensions for Distributed
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`
`254
`
`Adobe - Exhibit 1023, page 254
`
`