(.NET Core C#) 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.

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// 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.

// Apparently, SharePoint needs an "Accept" request header equal to "application/xml",
// otherwise SharePoint will return an utterly incomprehensible and useless error message.
string savedAccept = http.Accept;
http.Accept = "application/xml";

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

// Restore the default Accept header
http.Accept = savedAccept;

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"));