Transcript WWW-Authenticate

Servlets:
HTTP Request Header Contents
and Responses
HTTP Requests & Responses
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Road Map
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Recap and Overview
Reading HTTP Request Headers
Generating the Server Response
Case Study 1: Search Engines
Case Study 2: Basic Web Security
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Restricting by User Name/Password
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Recap and Overview
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Overview
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Interaction between browser and web
server.
Request
Web
Browser
Response
Web
Server
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Client Request Data
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When a user submits a browser request to a
web server, it sends two categories of data:
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Form Data: Data that the user explicitly typed
into an HTML form.
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For example: registration information.
HTTP Request Header Data: Data that is
automatically appended to the HTTP Request from
the client.
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For example: cookies, browser type, etc,
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Reading HTTP Request
Headers
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Sample HTTP Request
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A sample HTTP Request to Yahoo.com
GET / HTTP/1.1
Accept: */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)
Host: www.yahoo.com
Connection: Keep-Alive
Tip: Check out:
Cookie: B=2td79o0sjlf5r&b=2
http://www.web-sniffer.net
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Accessing HTTP Headers
As in the SnoopServlet Example:
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To access any of these Headers, use the
HTTPServletRequest getHeader() method.
For example:
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To retrieve a list of all the Header Names, use the
getHeaderNames() method.
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String connection = req.getHeader(“Connection”);
getHeaderNames() returns an Enumeration object.
For example:
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Enumeration enum = req.getHeaderNames();
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Additional HTTP Information
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getMethod()
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getRequestURI()
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Indicates the request method, e.g. GET or POST.
Returns the part of the URL that comes after the
host and port. For example, for the URL:
http://randomhost.com/servlet/search, the
request URI would be /servlet/search.
getProtocol()
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Returns the protocol version, e.g. HTTP/1.0 or
HTTP/1.1
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Reading Browser Types
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The User-Agent HTTP header indicates
the browser and operating system.
For example:
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user-agent Mozilla/4.0 (compatible; MSIE
6.0; Windows NT 5.1)
You can use this header to differentiate
browser types or simply log browser
requests.
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Example User-Agents
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Internet Explorer:
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Mozilla
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user-agent Mozilla/4.0 (compatible; MSIE
6.0; Windows NT 5.1)
Mozilla/5.0 (Windows; U; Windows NT 5.1;
en-US; rv:1.4) Gecko/20030624
For strange historical reasons, IE
identifies itself as “Mozilla”
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Generating the Server
Response
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Sample HTTP Response
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As a refresher, here’s a sample HTTP response:
HTTP/1.1 200 OK
Date: Mon, 06 Dec 2004 20:54:26 GMT
Server: Apache/1.3.6 (Unix)
Last-Modified: Fri, 04 Oct 2002 14:06:11 GMT
Content-length: 327
Connection: close
Content-type: text/html
<title>Sample Homepage</title>
<img src="/images/oreilly_mast.gif">
<h1>Welcome</h2>Hi there, this is a simple web page.
it may…
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Granted,
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Generating Responses
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Servlets can return any HTTP response
they want.
Useful for lots of scenarios:
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Redirecting to another web site.
Restricting access to approved users.
Specifying content-type other than
text/html.
Return images instead of HTML.
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Setting the HTTP Status Code
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Normally, your Servlet will return an HTTP Status
code of: 200 OK to indicate that everything went
fine.
To return a different status code, use the
setStatus() method of the HttpServletResponse
object.
Be sure to set the status code before sending any
document content to the client.
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Using setStatus()
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setStatus takes an integer value. But, it’s best to use the
predefined integers in the HttpServletResponse. Here are a
few:
SC_BAD_REQUEST
 Status code (400) indicating the request sent by the client
was syntactically incorrect.
SC_FORBIDDEN
 Status code (403) indicating the server understood the
request but refused to fulfill it.
SC_INTERNAL_SERVER_ERROR
 Status code (500) indicating an error inside the HTTP server
which prevented it from fulfilling the request.
SC_NOT_FOUND
 Status code (404) indicating that the requested resource is
not available. HTTP Requests & Responses
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Sending Redirects
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You can redirect the browser to a different URL by
issuing a Moved Temporarily Status Code:
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SC_MOVED_TEMPORARILY: Status code
(302) indicating that the resource has
temporarily moved to another location.
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Because this is so common, the HttpServletResponse
interface also has a sendRedirect() method.
 Example:
res.sendRedirect( “http://www.yahoo.com”);
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Example: Search Engines
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Multiple Search Engines
SearchEngines Servlet
 Enables users to submit a search query to
one of four search engines.
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Google
AllTheWeb
Yahoo
AltaVista, etc.
The code exploits the HTTP Response Header
to redirect the user to the correct search
engine.
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Architecture
“I want to search for
Bill Gates on Google”
SearchEngines
Servlet
“Go to Google”
Web
Browser
“I want to search for
Bill Gates on Google”
Google
“Your results…”
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SearchSpec.java
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The SearchSpec object contains information
about connecting to a specific search engine
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public String makeURL (String searchString, String
numResults)
You provide this method with a search string and
the number of results, and it returns the URL and
search query specific to Google, Yahoo, HotBot,
etc.
Class is contained in SearchEngines.java on acad
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SearchUtilities.java
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The SearchUtilities.java code has an
array of SearchSpec objects: one for
Google, one for Yahoo, etc.
It also provides a makeUrl method…
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SearchEngines.java
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The main servlet code.
This code:
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Extracts the searchEngine parameter.
If no such parameter exists, it sends an
HTTP Error.
Otherwise, it calls SearchUtilities to
construct the correct URL.
Finally, it redirects the user to this new
URL.
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Example: Basic Web Security
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HTTP Authentication
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The HTTP Protocol Includes a built-in
authentication mechanism.
Useful for protecting web pages or servlets
that require user name / password access.
First, let’s examine the basic mechanism and
the HTTP Headers involved.
Then, let’s figure out how to build a servlet
that exploits this mechanism.
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Basic Authentication
1)
If a web page is protected, the Web Server
will issue an authentication “challenge”:
HTTP/1.1 401 Authorization Required
Date: Sun, 27 Aug 2000 17:51:25 GMT
Server: Apache/1.3.12 (Unix) ApacheJServ/1.1 PHP/4.0.0
mod_ssl/2.6.6 OpenSSL/0.9.5a
WWW-Authenticate: BASIC realm="privileged-few"
Keep-Alive: timeout=90, max=150
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html
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WWW-Authenticate
WWW-Authenticate: BASIC realm=“realm"
 When you issue a return status code of 401,
“Authorization Required”, you need to tell the browser
what type of authentication is required.
 You do this via the WWW-Authenticate Header. This
header has two parameters:
 BASIC: Basic authorization requiring user name
and password.
 Realm: you can create multiple “realms” of
authentication for different users, e.g. “Admin”,
“User”, “Super_User”, etc.
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Basic Authentication Cont.
Upon receiving an authentication challenge, the
browser will prompt the user with a pop-up box
requesting the user name and password.
Browser takes the “username:password” from
the user and encrypts it using the Base 64
Encoding Algorithm.
2)
3)
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For example: if the string is “marty:martypd”, the Base 64
string is “bWFydHk6bWFydHlwdw==”
We will not cover the details of Base 64, but remember that
Base 64 is easy to decode. Therefore, even if your page is
protected, someone can easily intercept your Base 64
string and decode it.
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Basic Authentication Cont.
4)
The browser reissues the request for the
page. In the HTTP request, the browser
indicates the Authorization string:
GET /servlet/coreservlets.ProtectedPage HTTP/1.1
Accept: image/gif, */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)
Host: www.ecerami.com
Connection: Keep-Alive
Authorization: Basic bWFydHk6bWFydHlwdw==
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Basic Authentication Cont.
Web Server checks the user name and
password.
5.
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If User Name/Password is correct, web
server displays the protected page.
If the User Name/Password is incorrect,
web server issues a second
authentication challenge.
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Almost there…
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Before we examine the actual servlet
code, there are two pieces of Java
coding we need to examine:
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sun.misc.BASE64Decoder.
java.util.Properties
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Base 64 Encoding
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Sun provides a class called:
sun.misc.BASE64Decoder.
You can use the decodeBuffer() method to
decode the Base 64 String sent from the
user:
String userInfo = “bWFydHk6bWFydHlwdw==”
BASE64Decoder decoder = new BASE64Decoder();
String nameAndPassword =
new String(decoder.decodeBuffer(userInfo));
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After this code, nameAndPassword will be set to “marty:martypd”
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java.util.Properties
A utility class for reading in property files.
 For example, suppose you have the following
password.properties file:
#Passwords
#Sat Aug 26 11:15:42 EDT 2000
nathan=nathanpw
marty=martypw
lindsay=lindsaypw
bj=bjpw
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java.util.Properties
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You can easily and automatically load
the password file and parse its
contents:
passwordFile = "passwords.properties";
passwords = new Properties();
passwords.load(new FileInputStream(passwordFile));
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Then, you can extract the password for
a specific user name:
String password = properties.getProperty ("marty“);
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ProtectedPage.java
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Here’s how the Servlet Works:
1) Initialization: Read in a Password file of valid
user names and passwords.
2) Check for the HTTP Authorization Header.
3) Decode the Authorization Header using Base 64
to obtain user name and password.
4) Check the User Name and Password against the
valid names list.
 If valid, show protected page.
 Else, issue another authentication challenge.
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Form Authentication System
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BASE64 not secure
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Need secure solution!
Use HTML form
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Example: FormAuthenticate
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Access of servlet attempts to access protected data
User redirected to login form web page
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Example takes any combination
Once authenticated, redirected to desired page
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Session object used to store desired destination during
login diversion
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Summary
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Lots of hidden HTTP data, including
headers and cookies are sent from
browser to the server.
HTTP Header data can also be sent
from server to the browser, e.g. error
codes, redirection codes, etc.
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