Cross Site Authentication and Data Transfer
Published: 19 Dec 2007
In this article Tom presents a methodology for cross web site authentication (form authentication) and data transfer using ASP.NET 2.0, SQL Server 2005, web services, and Microsoft Enterprise Library.
by Tom Zhang
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With the increasing need of using third party services, such as e-commerce, convention registration, web content management, etc., transferring user (customer) data from our database to a third party service provider becomes more frequent and more complicated. Due to different data storage infrastructures and security restrictions, there is no direct communication between our database and the third party database. One way to transfer data is to develop a scheduled data sync process which generates data files (text files) and sends our data to the third party at certain time interval. This seems to be straight forward and simple. But it has several fundamental issues as listed below that cannot be easily resolved.

·         Sooner or later Data becomes out of sync.

·         Changes occurring in our database cannot be transferred to the third party until the next scheduled run. Therefore, the third party database is not up to date.

·         There is a need to create a different data transfer mechanism for each third party due to different business requirements. It is difficult to manage the multiple data sync processes.

·         Each third party has its own authentication process. Our users end up with several sets of user names and passwords. This is inconvenient for users and often confusing.

Cross site authentication (form authentication) and data transfer use a “single sign-on” approach in which the user is always brought to our authentication site to sign on. After being successfully authenticated, the user is then redirected to a third party site where the third party application calls our authentication web service to confirm the user’s authentication status and to retrieve a complete set of user data to update its database.

In this article I will share one methodology using ASP.NET form authentication with the development communities. Certainly there are better ways to do this than what I am about to discuss here. Please feel free to send your feedbacks. I would like to learn from you as well.

Basic Program Logic

The user clicks a formulated login link and he or she is sent to the authentication site. This link contains a QueryString parameter ReturnUrl that represents the landing page of a third party site to which the user will be redirected after being successfully authenticated. The login link looks like:

SiteID is a parameter that the authentication site uses to determine web page presentation style as well as data transfer logic (what stored procedure to use for delivering data to a third party site). Parameter1 and Parameter2 are a part of the ReturnUrl and are used by the third party site for its own purposes. The ReturnUrl should be UrlEncoded so that the whole string including parameters and any preserved characters like “?,” “=,” “&” is treated as one single parameter as the following:

The authentication site first obtains the SiteID and the ReturnUrl from QueryString and then presents the user, based on the SiteID, with a login page that has a graphic presentation similar to the third party site. The user enters his username and password, and clicks the login button. Upon a successful authentication, the application retrieves the user’s identity from the database and builds a securely encrypted url QueryString parameter, EncryptedData, that includes UserID, ExpirationDateTime and SiteID (more can be added as needed). It then appends it to the end of the ReturnUrl. The ReturnUrl now looks like:

The user is then redirected to the landing page of the third party site using the above ReturnUrl. The EncryptedData should be UrlEncoded.

At the third party site, the landing page grabs the parameter EncryptedData from QueryString and calls an authentication web service with it. The web service decrypts the parameter and checks the expiration date. Successful decryption with a valid expiration date signifies that the user has been authenticated. The web service then retrieves a complete set of user data from database using a stored procedure determined by the SiteID and returns the data to the third party application. The landing page inserts/updates user data in its own database and performs necessary actions to programmatically log the user into its system.

To illustrate how the cross site authentication works, I have prepared a demo application for download. The solution contains two web sites. One is the CrossSiteAuthentication that provides a login interface to authenticate users as well as a web service for a third party to consume. The other is the ThirdPartySite that simulates a third party service provider site. Although both sites are in the same solution and run on local machine, the methodology is applicable to any third party site located at a remote location.

To run the demo, you will need Sql Server 2005 Express Edition (make sure that the service is running. It may be necessary to test its connection from Server Explorer in Visual Studio 2005) and Microsoft Enterprise Library – January, 2006. The enterprise library is used for data access and cryptography. Since the security key for cryptography is machine dependent, you will need to create a key using Enterprise Library Configuration Utility that comes with the library installation. Use the following steps to create a key.

·         Start Enterprise Library Configuration Utility (under Start – All Programs, Microsoft Patterns & Practice, Enterprise Library – January 2006).

·         Right click on Enterprise Library Configuration root item and select New Application. Right click Application Configuration (a newly created item below the root), and select New, Cryptography Application Block. Right click Symmetric Providers and select New, Symmetric Algorithm Provider. In the dialog box that comes up, select TripleDESCryptoServiceProvider (This is the one I used. Others should all be fine.). In the key wizard dialog box, select Create New Key and click Next. Enter some text and click Generate, Next. Give a name (I used tripleDES.key) and save it to the CrossSiteAuthentication application folder (can be saved anywhere). Click Next, select Machine mode and click Finish.

·         Open web.config file in CrossSiteAuthentication application and change the element protectedKeyFilename inside symmetricCryptoProviders to the path where you saved the key.

In Visual Studio 2005, open the solution. Expand the ThirdPartySite tree, right click on the LandingPage1.aspx and select View in Browser. When the page appears, click “Check Authentication Status” button. You will see that the user is not authenticated. Close the browser. This action is to make the ThirdPartySite accessible by starting its local web server since it is a file-system based application. Expand the CrossSiteAuthentication tree. Right click Default.aspx page and select View in Brower. Two links are shown on the page. Looking at the HTML code for these two links, you will see that one has a ReturnUrl that points to Third Party #1 web site and another to Third Party #2 web site. In the demo they are not really two sites, but two pages in the ThirdPartySite application, LandingPage1.aspx and LandingPage2.aspx. Please check the port number in the links and make sure it is a correct number for the ThirdPartySite application.

Click the link "Third Party #1 Web Site," the login.aspx page shows up with a header image and header text of Site1. Enter the user name: johnd and pw: password (or janed/password, there are only two users in customer table), and click the Login button. You are authenticated and are redirected to the LandingPage1.aspx in the ThirdPartySite. The landing page calls web service and pulls out John Doe’s data, and programmatically logs John into the ThirdPartySite. Click the “Check Authentication Status” button. This time you will see that user is authenticated. If you change the "EncryptedData" in the Url or leave the page open for over a minute and then refresh the page, you will see a message indicating decryption failed or url expired.

Repeat the above steps with the Third Party #2 Web Site link on the default.aspx page (you will see a different header image and header text) and then you are redirected to the LandingPage2.aspx after being authenticated.

Cross Site Authentication Application

In the demo download, CrossSiteAuthentication is the "single sign-on" authentication site, consisting of a sql database, an login page and a master page, two classes, and a web service. Let us take a closer look at each one of them.


CustomerDB, a sql database, is the backend data storage for the application. There are two tables in the database, Customer and SiteInfo, and four stored procedures. The Customer table holds the user contact information including login credentials. The SiteInfo table specifies style information for each third party site as well as a stored procedure name for pulling a complete set of customer data for data transfer.

The four stored procedures are as follows:

·         Customer_Login - Verifies users' credentials and returns CustomerID and names. More fields may be added as needed.

·         SiteInfo_GetSiteInfo - Retrieves style information based on SiteID, such as style sheet name, header image path and header text, as well as a stored procedure name for data transfer.

·         Site1_GetCustomerInfo - Pulls a complete set of customer data for the third party #1 site. There is only one select statement in the stored procedure. However, more statements (with joins and conditions) can be added based on business requirements. Multiple sql statements will translate into multiple tables in a DataSet.

·         Site2_GetCustomerInfo - Retrieves data as the above for third party #2 site.


There are two classes in the CrossSiteAuthentication application: AuthenticationAssistant and CryptographyAssistant.

Three methods, as shown in Listing 1, in the AuthenticationAssistant class are of our interest. The VerifyCredentials method performs user credential verification and returns the user's identity and name as a SqlDataReader. The number of fields returned is based on the stored procedure - Customer_Login. The WellFormReturnUrl method creates a well formed ReturnUrl by properly appending an encrypted QueryString parameter to the original ReturnUrl. The RetrieveUserDataSet method pulls back a complete set of user data for transferring to a third party. The argument siteID determines what stored procedure to use. Code in each method is self explanatory.

Listing 1

public static SqlDataReader VerifyCredentials(string userName, string password)
  //confirm credentials upon success, return a single record for this user
  return ExecuteDataReader("Customer_Login", new object[]
    userName, password
//this method retrieves a complete set of user data that a third party app needs
public static DataSet RetrieveUserDataSet(int siteID, string CustomerID)
  //siteID determines storedproc name.
  DataSet ds = ExecuteDataSet(GetDataTransferProc(siteID), new object[]
  return ds;
//The return url to be used to send user back to a third party site needs to be 
//parsed to add an encrypted parameter properly
public static string WellFormReturnUrl(string originalReturnUrl, string
  string WellFormedUrl = "";
  //check if the original return url has parameters attached already
  int Position = originalReturnUrl.IndexOf("?");
  if (Position !=  - 1)
//? exists. original url has some parameters already, append the 
//ecryptedParameter to the end with a "&"
    WellFormedUrl = originalReturnUrl + "&EncryptedData=" +
  //original url does not have any parameters, append PmaInfo with "?"
    WellFormedUrl = originalReturnUrl + "?EncryptedData=" +
  return WellFormedUrl;

The CryptographyAssistant class does encryption and decryption. The encryption involves two steps. First of all, the user identity (in this case, CustomerID), name and other relevant data returned in a SqlDataReader during the user's credential verification need to be serialized into one single string. This is performed by the BuildUrlParameterString method as shown in Listing 2.

Listing 2

public string BuildUrlParameterString(string keyFieldName, SqlDataReader rd)
  //keyFieldName is the primary key such as userID, CustomerID, contactID etc.
  //This has to be included in the SqlDataReader
  if (_siteID == null)
    throw new Exception("SiteID property is not set.");
  bool ContainPrimaryKey = false;
  StringBuilder MyString = new StringBuilder();
  for (int i = 0; i < rd.FieldCount; i++)
    if (rd.GetName(i).ToLower() == keyFieldName.ToLower())
      ContainPrimaryKey = true;
  //check to make sure that "CustomerID" field exists
  if (!ContainPrimaryKey)
    throw new Exception("Primary key field - " + keyFieldName +
      " is not returned from database");
   //Add an expiration value to expire the string after a certain period of time
   // elapsed.
  //add siteID which is needed to get site information
  //last item does not need "&"
  return MyString.ToString();

This method basically loops through all fields in the SqlDataReader and concatenate field name and value pairs into a single string in the form of FieldName1=FieldValue1&FieldName2=FieldValue2, and so on. Since this parameter will be encrypted and appended to the end of a ReturnUrl, the field value should be UrlEncoded. ExpirationDateTime is included in the parameter string in order to expire it when a specified period of time elapses. The ExpirationDateTime is set by adding a few minutes (_validDurationInMinutes) to the current time. The _validDurationInMinutes has a default value of 2 minutes and can be changed through the exposed property ValidurationInMinutes. SiteID is also built into the string for later use in a web service call. As indicated earlier, since user data is passed in as a SqlDataReader, the number of fields in the string can be adjusted simply by changing the sql statement for the reader. However, since this is for the purpose of authentication, it is better to have less data unless more is absolutely required.

The second step is to encrypt the parameter string using Microsoft Enterprise Library as shown Listing 3.

Listing 3

public string EncryptText(string plainText)
  if (_securityProvider == null)
    throw new Exception("No security provider has been specified");
  return Cryptographer.EncryptSymmetric(_securityProvider, plainText);

The decryption is a reverse operation of the above. It also includes two steps. First, an encrypted string is passed into the DecryptText method to get decrypted. The GetNameValueCollection method then parses the name and value pairs contained in the decrypted string to create a user NameValueCollection object which is used in the web service. Decryption is also done using Microsoft Enterprise Library.

Listing 4

public string DecryptText(string encryptedText)
  if (_securityProvider == null)
    throw new Exception("No security provider has been specified");
  return Cryptographer.DecryptSymmetric(_securityProvider, encryptedText);
public NameValueCollection GetNameValueCollection(string serializedString)
  //reverse operation of the BuildUrlParameterString
  //Create a NameValueCollection from the serialized parameter string
  //which has the form of p1=value1&p2=value2...
  NameValueCollection MyCollection = new NameValueCollection();
  string[]NameValuePairs = serializedString.Split('&');
  for (int i = 0; i < NameValuePairs.Length; i++)
    string[]NameValue = NameValuePairs[i].Split('=');
    MyCollection.Add(NameValue[0], HttpUtility.UrlDecode(NameValue[1]));
  if (DateTime.Now > Convert.ToDateTime(MyCollection["ExpirationDateTime"]))
    throw new Exception("Url has expired. Please log in again.");
  return MyCollection;

Web Service

AuthenticationService.asmx is a web service for the landing page of a third party to consume in order to confirm a user’s authentication status and to transfer user data. Upon receiving the EncryptedData string (Request.QueryString[“EncryptedData”]), the third party landing page calls the RetrieveUserDataSet web method (or any other web method as needed) with the EncryptedData string. The web service utilizes the CryptographyAssistant class to decrypt the string and to return a user NameValueCollection object which contains the user identity. It then calls methods in the AuthenticationAssistant class to retrieve a complete set of user data using the values in the NameValueCollection object. During this process, if the EncryptedData is expired or tampered with, the decryption will fail.

The web service provides three web methods, as described below.

·         RetrieveUserDataSet - Decrypts the EncryptedData passed in by a third party caller. Upon success, it returns a complete set of user data as a DataSet. Upon failure, it returns a null and sends back an error messages in the reference parameter returnMessage.

·         RetrieveUserDataXml - Does the same thing as the above, but returns a complete set of user data as a serialized xml string.

·         RetrieveUserID - Decrypts the EncryptedData passed in by a third party caller. Upon success, returns UserID as a string. Upon failure, returns an empty string and sends back an error messages in the reference parameter returnMessage. If you do not need user data for transfer, but need only to confirm a user’s authentication status, this is the method to call.

The RetrieveUserDataSet and RetriveUserDataXml web methods return exactly the same data. The reason that two methods are exposed here is to accommodate non .NET third party applications in which a DataSet is not a recognized data type. Similarly, an error message is sent back to the caller through a reference parameter ReturnMessage instead of throwing an exception for the same reason. Depending on what platform a third party uses, more variation of methods may be needed to return data in the right formats for a particular third party application to consume.

Master Page and Login page

Graphic presentation style of the authentication site is achieved using a Master page, AuthMaster.master. The style is dynamically applied based on SiteID so that the authentication site looks similar to its target third party site. In the demo, the style is relatively simple. However, it does illustrate the methodology for more sophisticated graphic presentation.

There are two style sheets, two header images and two header texts which match two third party sites in the demo application (actually two landing pages) respectively. Code Listing 5 is the function that applies styles in the AuthMaster.master page. The variable TableWidth controls the display width of the page, and is directly placed on the master page in the HTML table tag (<Table Width=<%# TableWidth%>>) and, therefore, DataBind() needs to be called to bind the variable. The rest is either an server control (for example, imgHeader and lblHeaderText) or html server control (for example, MainStyle). Their properties change with SiteID.

Listing 5

private void ApplySiteStyle(int siteID)
  //retrieve site style information from database
  SqlDataReader rd = AuthenticationAssistant.ExecuteDataReader(
    "SiteInfo_GetSiteInfo"new object[]
  if (rd.Read())
    MainStyle.Href = rd["StyleSheetName"].ToString();
    imgHeader.ImageUrl = rd["HeaderImagePath"].ToString();
    imgHeader.Width = Unit.Pixel((int)rd["HeaderWidth"]);
    imgHeader.Height = Unit.Pixel((int)rd["HeaderHeight"]);
    lblHeaderText.Text = rd["HeaderText"].ToString();
    TableWidth = (imgHeader.Width == 0 ? "800" : imgHeader.Width.ToString());
  rd = null;

The login page basically does three things during the user authentication process.

·         Calls VerifyCredentials method in the AuthenticationAssistant class to check user credentials against user data in database, and returns the UserID and name in a SqlDataReader.

·         Serializes the user information returned during login with the expiration data time and SiteID, and then encrypts the serialized data string using the CryptographyAssistant class to create the EncryptedData QueryString parameter. The expiration time is set to be 1 minute from the current time, meaning that the EncryptedData will expire in 1 minute from the time user credentials are verified.

·         Redirect the user to a third party site using a "well formed" ReturnUrl.

The SiteID and ReturnUrl are requested in the Page_Load event and kept in two invisible labels, lblSiteID and lblReturnUrl (Label.Visible=false). Their values are used when the Login button is clicked. The code in the Login button click event is self explanatory as seen below.

Listing 6

SqlDataReader rd = null;
  rd = AuthenticationAssistant.VerifyCredentials(txtUserName.Text,
  if (rd.Read())
    CryptographyAssistant ca = new CryptographyAssistant();
    ca.ValidDurationInMinutes = 1;
    ca.SiteID = (lblSiteID.Text == ""null : lblSiteID.Text);
    ca.SecurityProvider = ConfigurationManager.AppSettings["SecurityProvider"];
    string EncryptedParameter = ca.EncryptText(ca.BuildUrlParameterString(
      "CustomerID", rd));
//Append the encrypted string to the end of the ReturnUrl and then redirect 
//the user to the third party site
      (lblReturnUrl.Text, EncryptedParameter));
    lblError.Text = "No user with these credentials has been found.";
catch (Exception ex)
  lblError.Text = ex.Message.ToString();
  if (rd != null)
    rd = null;
Third Party Site

The application ThirdPartySite simulates a remote third party site as the target site that a user is redirected to upon a successful authentication. As mentioned before, a landing page at the ThirdPartySite receives an EncryptedData string from Url and then consumes the authentication web service which decrypts the string and returns a complete set of user data. The third party application then processes the data returned and updates its database, and then programmatically logs the user into its site. If the decryption fails because of either the EncryptedData being expired or tampered with, an error message is returned to the third party application. As a demo, the user data returned to the third party is not saved into a database but displayed in a GridView.

A web reference pointing to CrossSiteAuthentication/AuthenticationService.asmx in the same solution is added to the site and named as AuthenticationService. There are two landing pages in the application simulating two different third party sites. For the demo, the code in LandingPage1.aspx and LandingPage2.aspx is exactly the same. Therefore, we only need to take a look at LandingPage1.aspx. Looking at the code in Listing 7, the page gets the EncryptedData from QueryString and requests for Parameter1 and Parameter2 which are used by the third party for its own purpose. For the demo, any code involving Parameter1 and Parameter2 are omitted. The page then declares an instance of the AuthenticationService and calls the RetrieveUserDataSet web method. If a DataSet is returned, signifying the success of the cross site authentication, this page performs necessary actions to handle the user data, and then logs the user in programmatically. Otherwise, authentication fails and an error message is displayed.

Listing 7

//request for the EncryptedData
string EncryptedData = Request.QueryString["EncryptedData"];
if (EncryptedData == null)
  lblError.Text = "A required parameter is missing from url. ";
  return ;
//Request p1 and p2 from Url. p1 and p2 are the parameters that 
//the third party app needs
string p1 = Request.QueryString["Parameter1"].ToString();
string p2 = Request.QueryString["Parameter2"].ToString();
//additional code here to process the parameters
//Add a web reference to your app and name it anything you like. Here it is 
//named as AuthenticationService.
//declare web service and a reference variable - ReturnMessage
AuthenticationService.AuthenticationService AuthService = new
string ReturnMessage = "";
DataSet ds = null;
//Call Web Method: RetrieveUserDataSet
//success: user authenticated, get a DataSet.
//Failure: user not authenticated or Url expired. Return null and error message.
  ds = AuthService.RetrieveUserDataSet(ref ReturnMessage, EncryptedData);
catch (Exception ex)
  lblError.Text += ex.Message.ToString();
if (ReturnMessage != "")
  lblError.Text += ReturnMessage;
  return ;
if (ds != null)
  gvUserData.DataSource = ds.Tables[0];



I have discussed the methodology for cross site authentication and data transfer. The demo application is a greatly simplified version in order to illustrate the concept. In the real world, at least several additional parts have to be in place, such as "Remember Me," "Forgot My Password," "Create New Account," etc.  In addition, the accessibility of the web service should be restricted to the third parties that you have a partnership with. Depending on the programming platform that a third party uses, more variations of a web method may be required to return data in an appropriate format (for example, a string array or a special character like "|" separated string, etc.) that the third party can process.

This methodology is not necessarily a good solution, rather a topic for discussion. Your comments are appreciated.

User Comments

Title: How to use key   
Name: Harsh
Date: 2012-09-07 5:11:25 AM

That .key file not working properly.
I am getting this error,"Key not valid for use in specified state."

Title: Re : Can we use this to connect to a SAP IView   
Name: Kalpesh
Date: 2009-11-11 12:50:26 AM
Hi Tom,

Thank you very much for your kind reply.

I looked in .Net connector in past, but my approach is quite different. Basically, I just want to show the IView which is already there in SAP, for that I just need to authenticate myself. But any way I will look in to both your suggestions.

Thanks again.
Title: Connect to a SAP IView   
Name: Tom
Date: 2009-11-10 8:46:21 AM
Hi Kalpesh,

With this method, basically, you need to code a landing page in your target application. If you can't do it in SAP, this will not be suitable. I have not used SAP. By reviewing some documentation, it seems that SAP has a .NET connector which you may look into it. Here is an article: If you are able to do custom coding in SAP, I have newer version: in which encryption is replaced by a database table. See which method is a better fit.
Title: Can we use this to connect to a SAP IView   
Name: Kalpesh
Date: 2009-11-10 1:55:52 AM
Hi tom,
First of all..nice article.

I have one question regarding my requirement. I have one URL which points to the SAP IView. I also have the credentials to access this SAP site.

I have accessed/displayed that SAP IView in sharepoint using it's SSO service. Now I want to show the same thing in ASP.NET application. So can I implement the SSO(which you have given)in my application to view SAP IView.
Title: das   
Name: satya
Date: 2009-08-10 5:46:34 AM
hi i want to download this
Title: Reply: SSO from two server?   
Name: Tomz
Date: 2009-04-16 9:55:39 AM
If your two applications are running on the same second level domain, for example (, are both third level domains that belong to the same second level domain, you can write a cookie with the domain attribute of Both applications will be able to read the cookie. see this article:

If they are not on the same second level domain, you may try the methodology indicated in this article or the revised version at: The revised makes the implementation easier by removing encryptography.

Title: SSO from two server?   
Name: mrnothing
Date: 2009-04-16 4:26:01 AM
I have two application on two server
I can't get session, cokie, ..etc. when user login from one application and don't login again from another. Please help me!
Title: RE: how two webservices transfer data   
Name: Tom Z
Date: 2009-01-13 8:56:13 AM

Creating and consume an web service is relatively easy with Visual Studio. Here are some links:

Inside a web service, you just write your method like you write a method in a regular class.

To call the web service from another program in Visual studio, what you need to do is to add a WEB REFERENCE to your application (similar to using a class by adding a REFERENCE to your application), and then call the method like you call a method in a regular class.

Hope this helps. Thanks,
Title: how two webservices transfer data   
Name: zenab
Date: 2009-01-12 11:39:35 PM
kindly tell me any link in which full procedure is given to show how to develop a webservice in and how both web services transfer data to each other.
Awaiting for your kind response.
Title: Why redirecting when using a webservice?   
Name: Tom Z
Date: 2008-02-06 11:49:50 AM
Hi Dave,
Thanks for your invaluable input on this topic.

No doubt that a third party can consume the web service to authenticate a user directly without going to a centralized authentication site as introduced in this article. The reasons that I choose not to do it that way include the following:
- Minimize the amount of work that a third party has to do for authentication and data transfer;
- Reduce the complexity related to finding an existing record and creating a new record. An existing user does not initially reside in the third party database (only in our database). It will be a complicated process (or a lengthy process) for the third party app to find a user in our database through web service calls. If the “finding” process is not implemented, all existing users in our database would become “new” users at the third party site. When creating a new record, the third party not only needs to create a record for itself but also to collect additional information for our specific needs and then exports this record into our database. For example, let’s say the main business type of a user is required in our database, the third party has to create this field in its database, even though it does not need this information at all.

Regarding the length of URL as well as redirecting user between authentication site and a third party site, you have valid points. However, this method is intended to be used among business partners with “trusted” relationship. The issues can be resolved through the partnership.

Thinking of Windows Live solution, would that be similar to this? The difference is that Windows Live only does authentication while this method does both authentication and data transfer. In addition, Windows Live may not need web service calls (I guess) during authentication since “Live” components come with the Windows installation.

Title: Why redirecting when using a webservice?   
Name: Dave
Date: 2008-02-01 7:05:05 PM
It might sound silly, why not letting the third party websites consuming the webservice AuthenticationService.asmx?

It also has some other benefits:
- The user won't be redirected to another website
- you can return all kind of information, not needed to encrypt it.
- The authentication srevice itself can be secured by passing a SiteID an a pre-shared key. Other method is IP-based access.
- No problems redirecting from HTTPS (I assume registration / login is done over SSL!) to http and browser security warnings. Because the login page is on the website self, it makes much more sense to purchase a SSL certificate.

Of course you need to implemented a few pages such as registration, forget/change password, logout etc. But the authentication 'website' doesn't need to implement a new masterpage for each site which wants to use the service.

Another issues which might can be a problem is the use of EncryptedData in the url. More and more webservers have limits on the values of a query-string parameter. Because the returned information set can become very large, it might cause problems. On our webservers (both IIS and Apache) the maximum limit of query string parameters is set to 128 bytes. Exceeding the limit results in a 414 Request-URI too long.

Another issue, partly raised earlier, is that your sending the visitor to an website where it doesn't want to be. These days there are a lot of phissing websites. Redirecting a visitor from to can cause a visitor to leave your website permanently because he doesn't trust your website.

Webservices can also be consumed by other languages such as classic ASP , PHP and Java. And because each website is implementing it's own profile pages, it's also easier to implement an ajax-enabled forget password page for a specific website. Remember, ajax is not cool for WAP (mobile) sites.
Title: Well done   
Name: foton
Date: 2007-12-20 12:57:29 PM
Clearly written and explained. Lots of players making big bucks marketing variations on this method. Your article will give us the jump-start we need to do this in-house.

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