(Objective-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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#import <CkoFileAccess.h>
#import <CkoXml.h>
#import <CkoDateTime.h>
#import <NSString.h>
#import <CkoHttp.h>
#import <CkoHttpResponse.h>

// 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.
CkoFileAccess *fac = [[CkoFileAccess alloc] init];
CkoXml *xml = [[CkoXml alloc] init];
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>
// 

CkoDateTime *dtExpire = [[CkoDateTime alloc] init];
CkoDateTime *dtNow = [[CkoDateTime alloc] init];

NSString *formDigestXmlFile = @"qa_data/sharepoint/savedFormDigestValue.xml";
if ([fac FileExists: formDigestXmlFile] == YES) {

    [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: NO];
    int tExpire = [dtExpire GetAsUnixTime: NO];

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

}

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

CkoHttp *http = [[CkoHttp alloc] init];

// 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 = YES;

// 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.
NSString *savedAccept = http.Accept;
http.Accept = @"application/xml";

// Note: The last argument ("utf-8") is meaningless here because the body is empty.
CkoHttpResponse *resp = [http PostXml: @"https://SHAREPOINT_HTTPS_DOMAIN/_api/contextinfo" xmlDoc: @"" charset: @"utf-8"];
if (http.LastMethodSuccess != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

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

if ([resp.StatusCode intValue] != 200) {
    // A response status code not equal to 200 indicates failure.
    NSLog(@"%@%d",@"Response status code = ",[resp.StatusCode intValue]);
    NSLog(@"%@",@"Response body:");
    NSLog(@"%@",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.
CkoXml *xml2 = [[CkoXml alloc] init];

xml2.Tag = @"savedFormDigestValue";
[xml2 NewChild2: @"d:FormDigestValue" content: [xml GetChildContent: @"d:FormDigestValue"]];

int timeoutInSec = [[xml GetChildIntValue: @"d:FormDigestTimeoutSeconds"] intValue];
NSLog(@"%@%d",@"Timeout in seconds = ",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: [NSNumber numberWithInt: timeoutInSec]];
[xml2 NewChild2: @"d:ExpireDateTime" content: [dtExpire GetAsTimestamp: NO]];

// Persist the digest and expire time to a file.
[xml2 SaveXml: formDigestXmlFile];

NSLog(@"%@",@"Here is the new form digest value:");
NSLog(@"%@%@",@"X-RequestDigest: ",[xml GetChildContent: @"d:FormDigestValue"]);