Permission to provision new site collection through workflow - access-denied

Question

I am stuck onto a very strange situation.
I have a workflow that i use to provision new site on my web application. This workflow uses one custom workflow activity to provision the site using followoing statement.
---other code omited for clarity----
SPSiteCollection.Add()
This statement is throwing followign exception when my applicaiton pool account is not same as Central Admin applicaiton pool account.
Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
at
Microsoft.SharePoint.SPGlobal.HandleUnauthorizedAccessException(UnauthorizedAccessException
ex) at
Microsoft.SharePoint.Library.SPRequest.CreateSite(Guid
gApplicationId, String bstrUrl, Int32
lZone, Guid gSiteId, Guid gDatabaseId,
String bstrDat
after a lot of googling and findings i have zeroed down to the Applicaiton Pool account permission.
The workflow code always runs under the System account (the applicaiton pool identity). In order to create new SharePoint site collection, the application pool requires access to "SharePoint_Config" database.
When my web application is running under the applicaiton pool credential of Central Admin, it has all the access to the configuration database. But when i am running the under any other applicaiton pool identity which has less permission. it throws exception, even if i give DBO permission to the applicaiton pool account in the Configuration database.
My applicaiton event log has following entry :-
Event Source: Windows SharePoint
Services 3 Event Category: Database
Event ID: 3760 Date: 2/3/2010
Time: 2:36:16 AM User: N/A
Computer: SHAREPOINT20 Description:
SQL Database 'SharePoint_Config' on
SQL Server instance 'houspsr001' not
found. Additional error information
from SQL Server is included below.
Cannot open database
"SharePoint_Config" requested by the
login. The login failed. Login failed
for user 'DOMAIN\WebAppPool'.
For more information, see Help and
Support Center at
http://go.microsoft.com/fwlink/events.asp.
My question is...is it mendatory to run such code under the applicaiton pool account of central admin.
Any workaround for this....?
My question

Answer 1

Finally the access denied issue has been resolved. As I motioned in my previous email, the issue was due to insufficient permission to my application pool identity.
Central Admin was running under a different application pool identity
Web applications are running under a different application pool identity.
My workflow was using the ElevatedPrevilages to provision a site collection, and it used to get Access Denied from the database since it did not had permission to modify SharePoint_Config database.
Resolution
In order to resolve this issue i had to impersonate the application pool identity of Central Admin. Here is the required method for impersonating Central Admin application pool user.
#region Application Pool Identity Impersonate
protected static WindowsIdentity CreateIdentity(string User, string Domain, string Password)
{
// The Windows NT user token.
IntPtr tokenHandle = new IntPtr(0);
const int LOGON32_PROVIDER_DEFAULT = 0;
const int LOGON32_LOGON_NETWORK = 3;
tokenHandle = IntPtr.Zero;
// Call LogonUser to obtain a handle to an access token.
int returnValue = LogonUser(User, Domain, Password,LOGON32_LOGON_NETWORK, LOGON32_PROVIDER_DEFAULT,out tokenHandle);
//Check if the logon user method succeeded
if (returnValue <= 0)
{
int ret = Marshal.GetLastWin32Error();
throw new Exception("LogonUser failed with error code: " + ret);
}
//System.Diagnostics.Debug.WriteLine("Created user token: " + tokenHandle);
//The WindowsIdentity class makes a new copy of the token.
//It also handles calling CloseHandle for the copy.
WindowsIdentity id = new WindowsIdentity(tokenHandle);
CloseHandle(tokenHandle);
return id;
}
[DllImport("advapi32.dll", SetLastError = true)]
public static extern int LogonUser(
string lpszUsername,
string lpszDomain,
string lpszPassword,
int dwLogonType,
int dwLogonProvider,
out IntPtr phToken
);
[DllImport("advapi32.dll", SetLastError = true)]
public static extern int ImpersonateLoggedOnUser(
IntPtr hToken
);
[DllImport("advapi32.dll", SetLastError = true)]
static extern int RevertToSelf();
[DllImport("kernel32.dll", SetLastError = true)]
static extern int CloseHandle(IntPtr hObject);
#endregion
And then my code to create site collection looks like:-
//Impersonate the logged in user, ApplicationUser, LoginDomain and Password are exposed as property of the class.
WindowsImpersonationContext wiContext = CreateIdentity(this.ApplicationPoolUser, this.LoginDomain, this.SystemPassword).Impersonate();
//Provision new site collection and update the property for new site collection url.
using (SPSite newSiteCollection = spSiteColl.Add(SUGGESTEDURL, TITLE, DESC, LCID, WEBTEMPLATE, PRIMARYOWNER.LoginName, PRIMARYOWNER.Name, PRIMARYOWNER.Email, SECONDARYOWNER.LoginName, SECONDARYOWNER.Name, SECONDARYOWNER.Email))
{
this.SUGGESTEDURL = newSiteCollection.Url;
}
//Reset the impersonation.
wiContext.Undo();

Answer 2

As Im not allowed to comment on Sudhir's answer, Im posting my remark as an answer. I used basically the same code which Sudhir proposes as a solution. The impersonation works, but it has a security flaw. If you store your password as a plain text (managed) string it may be moved within memory and even stored to the hard disk because of paging. This makes it easy for aunothrized persons to spy your credentials.
It is therefor recommended to use SecureString for this purpose. How this can be used in conjunction with SecureString can be looked up on MSDN. The main difference to Sudhir's solution is to use a different overload of LogonUser, namely
[DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
internal static extern bool LogonUser(String username, String domain,
IntPtr password, int logonType,
int logonProvider, ref IntPtr token);
and use it like this (this code is from MSDN):
// Marshal the SecureString to unmanaged memory.
passwordPtr = Marshal.SecureStringToGlobalAllocUnicode(pwdSecureString);
// Call LogonUser, passing the unmanaged (and decrypted) copy of
// the SecureString password.
returnValue = LogonUser(userName, domainName, passwordPtr,
LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,
ref tokenHandle);
// Zero-out and free the unmanaged string reference.
Marshal.ZeroFreeGlobalAllocUnicode(passwordPtr);
This way the password is only encrypted right before we use it to do the user login. Afterwards the plaintext password is freed from memory immediatelly.