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Rob's SQL Server Blog

... SQL Server thoughts from the field

November 2011 - Posts

  • Enabling Kerberos Authentication for Reporting Services

    Recently, I’ve helped several customers with Kerberos authentication problems with Reporting Services and Analysis Services, so I’ve decided to write this blog post and pull together some useful resources in one place (there are 2 whitepapers in particular that I found invaluable configuring Kerberos authentication, and these can be found in the references section at the bottom of this post). In most of these cases, the problem has manifested itself with the Login failed for User ‘NT Authority\Anonymous’ (“double-hop”) error.

    By default, Reporting Services uses Windows Integrated Authentication, which includes the Kerberos and NTLM protocols for network authentication. Additionally, Windows Integrated Authentication includes the negotiate security header, which prompts the client to select Kerberos or NTLM for authentication. The client can access reports which have the appropriate permissions by using Kerberos for authentication. Servers that use Kerberos authentication can impersonate those clients and use their security context to access network resources.

    You can configure Reporting Services to use both Kerberos and NTLM authentication; however this may lead to a failure to authenticate. With negotiate, if Kerberos cannot be used, the authentication method will default to NTLM. When negotiate is enabled, the Kerberos protocol is always used except when:

    • Clients/servers that are involved in the authentication process cannot use Kerberos.
    • The client does not provide the information necessary to use Kerberos.

    An in-depth discussion of Kerberos authentication is beyond the scope of this post, however when users execute reports that are configured to use Windows Integrated Authentication, their logon credentials are passed from the report server to the server hosting the data source. Delegation needs to be set on the report server and Service Principle Names (SPNs) set for the relevant services. When a user processes a report, the request must go through a Web server on its way to a database server for processing. Kerberos authentication enables the Web server to request a service ticket from the domain controller; impersonate the client when passing the request to the database server; and then restrict the request based on the user’s permissions. Each time a server is required to pass the request to another server, the same process must be used.

    Kerberos authentication is supported in both native and SharePoint integrated mode, but I’ll focus on native mode for the purpose of this post (I’ll explain configuring SharePoint integrated mode and Kerberos authentication in a future post). Configuring Kerberos avoids the authentication failures due to double-hop issues. These double-hop errors occur when a users windows domain credentials can’t be passed to another server to complete the user’s request. In the case of my customers, users were executing Reporting Services reports that were configured to query Analysis Services cubes on a separate machine using Windows Integrated security. The double-hop issue occurs as NTLM credentials are valid for only one network hop, subsequent hops result in anonymous authentication.

    image

    The client attempts to connect to the report server by making a request from a browser (or some other application), and the connection process begins with authentication. With NTLM authentication, client credentials are presented to Computer 2. However Computer 2 can’t use the same credentials to access Computer 3 (so we get the Anonymous login error). To access Computer 3 it is necessary to configure the connection string with stored credentials, which is what a number of customers I have worked with have done to workaround the double-hop authentication error.

    However, to get the benefits of Windows Integrated security, a better solution is to enable Kerberos authentication. Again, the connection process begins with authentication. With Kerberos authentication, the client and the server must demonstrate to one another that they are genuine, at which point authentication is successful and a secure client/server session is established.

    image

    In the illustration above, the tiers represent the following:

    • Client tier (computer 1): The client computer from which an application makes a request.
    • Middle tier (computer 2): The Web server or farm where the client’s request is directed. Both the SharePoint and Reporting Services server(s) comprise the middle tier (but we’re only concentrating on native deployments just now).
    • Back end tier (computer 3): The Database/Analysis Services server/Cluster where the requested data is stored.

    In order to enable Kerberos authentication for Reporting Services it’s necessary to configure the relevant SPNs, configure trust for delegation for server accounts, configure Kerberos with full delegation and configure the authentication types for Reporting Services. These steps are outlined in greater detail in the "Manage Kerberos Authentication Issues in a Reporting Services Environment" whitepaper in the resources section at the end of this article.

    Service Principle Names (SPNs) are unique identifiers for services and identify the account’s type of service. If an SPN is not configured for a service, a client account will be unable to authenticate to the servers using Kerberos. You need to be a domain administrator to add an SPN, which can be added using the SetSPN utility. For Reporting Services in native mode, the following SPNs need to be registered

    --SQL Server Service
    SETSPN -S mssqlsvc/servername:1433 Domain\SQL

    For named instances, or if the default instance is running under a different port, then the specific port number should be used.

    --Reporting Services Service
    SETSPN -S http/servername Domain\SSRS
    SETSPN -S http/servername.domain.com Domain\SSRS

    The SPN should be set for the NETBIOS name of the server and the FQDN. If you access the reports using a host header or DNS alias, then that should also be registered

    SETSPN -S http/www.reports.com Domain\SSRS

    --Analysis Services Service
    SETSPN -S msolapsvc.3/servername Domain\SSAS

    Next, you need to configure trust for delegation, which refers to enabling a computer to impersonate an authenticated user to services on another computer:

    Location

    Description

    Client

    1. The requesting application must support the Kerberos authentication protocol.

    2. The user account making the request must be configured on the domain controller. Confirm that the following option is not selected: Account is sensitive and cannot be delegated.

    Servers

    1. The service accounts must be trusted for delegation on the domain controller.

    2. The service accounts must have SPNs registered on the domain controller. If the service account is a domain user account, the domain administrator must register the SPNs.

    In Active Directory Users and Computers, verify that the domain user accounts used to access reports have been configured for delegation (the ‘Account is sensitive and cannot be delegated’ option should not be selected):

    image

    We then need to configure the Reporting Services service account and computer to use Kerberos with full delegation:

     image

    image

    We also need to do the same for the SQL Server or Analysis Services service accounts and computers (depending on what type of data source you are connecting to in your reports).

    Finally, and this is the part that sometimes gets over-looked, we need to configure the authentication type correctly for reporting services to use Kerberos authentication. This is configured in the Authentication section of the RSReportServer.config file on the report server.

    <Authentication>

    <AuthenticationTypes>

              <RSWindowsNegotiate/>

    </AuthenticationTypes>

    <EnableAuthPersistence>true</EnableAuthPersistence>

    </Authentication>

    This will enable Kerberos authentication for Internet Explorer. For other browsers, see the link below. The report server instance must be restarted for these changes to take effect.

    Once these changes have been made, all that’s left to do is test to make sure Kerberos authentication is working properly by running a report from report manager that is configured to use Windows Integrated authentication (either connecting to Analysis Services or SQL Server back-end).

    Resources:

    Manage Kerberos Authentication Issues in a Reporting Services Environment
    http://download.microsoft.com/download/B/E/1/BE1AABB3-6ED8-4C3C-AF91-448AB733B1AF/SSRSKerberos.docx

    Configuring Kerberos Authentication for Microsoft SharePoint 2010 Products
    http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=23176

    How to: Configure Windows Authentication in Reporting Services
    http://msdn.microsoft.com/en-us/library/cc281253.aspx

    RSReportServer Configuration File
    http://msdn.microsoft.com/en-us/library/ms157273.aspx#Authentication

    Planning for Browser Support
    http://msdn.microsoft.com/en-us/library/ms156511.aspx

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