(C# UWP/WinRT) SharePoint -- Get Server Form Digest Value

Demonstrates how to get a server form digest value to be placed in the X-RequestDigest HTTP request header for POST, PUT, MERGE, and DELETE requests. A form digest value is typically valid for 1800 seconds (i.e. 30 minutes). This example persists the value to a file, and only requests a new form digest value if the existing one is near expiration.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

//  This requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  First, let's see if we already have a persisted form digest value
//  that hasn't yet expired.
Chilkat.FileAccess fac = new Chilkat.FileAccess();
Chilkat.Xml xml = new Chilkat.Xml();
bool success;

//  My example code (below) persists the form digest XML in this format:
// 
//  	<savedFormDigestValue>
//  	<d:ExpireDateTime>2017-04-12T20:46:39Z</d:ExpireDateTime>
//  	<d:FormDigestValue>0x3059FFB920651834540F3E6792EA73F5746B302E953FF4E808E485DB1E6C2836C7CF924644995F092453B02A94DE14A7962674B7B16780AF16EAFB8C246BCDC7,12 Apr 2017 17:08:22 -0000</d:FormDigestValue>
//  	</savedFormDigestValue>
// 

Chilkat.CkDateTime dtExpire = new Chilkat.CkDateTime();
Chilkat.CkDateTime dtNow = new Chilkat.CkDateTime();

string formDigestXmlFile = "qa_data/sharepoint/savedFormDigestValue.xml";
if (fac.FileExists(formDigestXmlFile) == true) {

    xml.LoadXmlFile(formDigestXmlFile);

    //  Get the expire date/time
    dtExpire.SetFromTimestamp(xml.GetChildContent("d:ExpireDateTime"));

    //  Get the current date/time
    dtNow.SetFromCurrentSystemTime();

    //  Get both times as Unix time values
    int tNow = dtNow.GetAsUnixTime(false);
    int tExpire = dtExpire.GetAsUnixTime(false);

    //  If tNow >= tExpire, then fall through.
    //  Otherwise, just use the cached digest value.
    if (tNow < tExpire) {
        Debug.WriteLine("Cached digest value is not yet expired.");
        Debug.WriteLine("X-RequestDigest: " + xml.GetChildContent("d:FormDigestValue"));
        return;
    }

}

//  If we got to this point, the cached digest value either does not exist, or expired.

Chilkat.Http http = new Chilkat.Http();

//  If SharePoint Windows classic authentication is used, then set the
//  Login, Password, LoginDomain, and NtlmAuth properties.
http.Login = "SHAREPOINT_USERNAME";
http.Password = "SHAREPOINT_PASSWORD";
http.LoginDomain = "SHAREPOINT_NTLM_DOMAIN";
http.NtlmAuth = true;

//  The more common case is to use SharePoint Online authentication (via the SPOIDCRL cookie).
//  If so, do not set Login, Password, LoginDomain, and NtlmAuth, and instead
//  establish the cookie as shown at SharePoint Online Authentication

//  When creating, updating, and deleting SharePoint entities, we'll need
//  to first get the server's form digest value to send in the X-RequestDigest header.
//  This can be retrieved by making a POST request with an empty body to
//  http://<site url>/_api/contextinfo and extracting the value of the
//  d:FormDigestValue node in the XML that the contextinfo endpoint returns.

//  Note: The last argument ("utf-8") is meaningless here because the body is empty.
Chilkat.HttpResponse resp = await http.PostXmlAsync("https://SHAREPOINT_HTTPS_DOMAIN/_api/contextinfo","","utf-8");
if (http.LastMethodSuccess != true) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

if (resp.StatusCode != 200) {
    //  A response status code not equal to 200 indicates failure.
    Debug.WriteLine("Response status code = " + Convert.ToString(resp.StatusCode));
    Debug.WriteLine("Response body:");
    Debug.WriteLine(resp.BodyStr);

    return;
}

xml.LoadXml(resp.BodyStr);

//  The response XML looks like this:

//  <?xml version="1.0" encoding="utf-8" ?>
//  <d:GetContextWebInformation xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices" xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata" xmlns:georss="http://www.georss.org/georss" xmlns:gml="http://www.opengis.net/gml" m:type="SP.ContextWebInformation">
//      <d:FormDigestTimeoutSeconds m:type="Edm.Int32">1800</d:FormDigestTimeoutSeconds>
//      <d:FormDigestValue>0x3059FFB920651834540F3E6792EA73F5746B302E953FF4E808E485DB1E6C2836C7CF924644995F092453B02A94DE14A7962674B7B16780AF16EAFB8C246BCDC7,12 Apr 2017 17:08:22 -0000</d:FormDigestValue>
//      <d:LibraryVersion>15.0.4569.1000</d:LibraryVersion>
//      <d:SiteFullUrl>https://SHAREPOINT_HTTPS_DOMAIN</d:SiteFullUrl>
//      <d:SupportedSchemaVersions m:type="Collection(Edm.String)">
//          <d:element>14.0.0.0</d:element>
//          <d:element>15.0.0.0</d:element>
//      </d:SupportedSchemaVersions>
//      <d:WebFullUrl>https://SHAREPOINT_HTTPS_DOMAIN</d:WebFullUrl>
//  </d:GetContextWebInformation>
// 

//  Cache the digest value, and also an expiration time.  If this code is run again
//  before the digest expires, we'll just get it from the file.
Chilkat.Xml xml2 = new Chilkat.Xml();

xml2.Tag = "savedFormDigestValue";
xml2.NewChild2("d:FormDigestValue",xml.GetChildContent("d:FormDigestValue"));

int timeoutInSec = xml.GetChildIntValue("d:FormDigestTimeoutSeconds");
Debug.WriteLine("Timeout in seconds = " + Convert.ToString(timeoutInSec));

//  Convert this to an expire timestamp.
//  Let's make it expire 30 seconds prior to the actual timeout, just to be safe.
if (timeoutInSec > 30) {
    timeoutInSec = timeoutInSec - 30;
}

dtExpire.SetFromCurrentSystemTime();
dtExpire.AddSeconds(timeoutInSec);
xml2.NewChild2("d:ExpireDateTime",dtExpire.GetAsTimestamp(false));

//  Persist the digest and expire time to a file.
xml2.SaveXml(formDigestXmlFile);

Debug.WriteLine("Here is the new form digest value:");
Debug.WriteLine("X-RequestDigest: " + xml.GetChildContent("d:FormDigestValue"));