Consume SharePoint Online CSOM (REST API) With .NET Core 3.1

Introduction 

 

This article will cover, How to consume Sharepoint online CSOM (REST API) operation using .NET Core 3.1 framework into a console application.

  

The topic needs to cover here:

1. Create Azure AD Instance with Delegate Permission.
2. Create Console Application and Add Microsoft.SharePointOnline.CSOM Nuget Package.
3. Add Authentication Manager Class to generate the access token.
4. Get Access Token & access SharePoint Online List data 

Step 1 - Create Azure AD Instance with Delegate Permission

 

Note

Users should have access to Azure Active Directory.

• Login to https://portal.azure.com
• Search and Select Azure Active Directory 

Once the user selects Azure AD, the App registration page will appear.

1. Select App registrations
2. Select +New registration 

 

Once the user selects new registration, add below details

1. Name "spocsom-api", user can add as per project namespace or naming convention guidelines.
2. Select "Account in this organization (single-tenant)
3. Click on the Register button 

 

 

Grant access to SharePoint Online.

1. Select API Permission
2. Click to Add Permission
3. Search and Add SharePoint from Request API Permission 

 

Delegate Permission, It required where user application needs to access data as the signed-in user.

1. Select Add a Permission
2. Selection Delegate Permission
3. Search and Select Sites 
4. Choose "All Site.Read" -> This is not site specific but quite secure , It will just come into use to generate token, not going to grant access to the site to access the content.
5. Click to "Add Permission" 

 

Grant Admin Consent

 

Grant permission by admin or user as part of the consent process.

1. Select "Grant admin consent for default directory and click ok to proceed.
2. All added api will show granted admin consent on behalf of the user. so it will not prompt for consent. 

 

Allow Public Client Flows

 

The app is going to collect username and password into plain text, so it should allow to yes.

1. Select authentication and scroll down till the end
2. Under advance settings -> select Allow Public client flows -> Select Yes -> Click on Save to Proceed.

 

Step 2 - Create Console Application and Add Microsoft.SharePointOnline.CSOM Nuget Package

1. Login to Visual Studio 2019 and Create New Project
2. Select ConsoleApp (.Net Core) and Ok to proceed. 

 

Install NuGet Package

 

Select solution and right-click on dependencies and NuGet Packages

 

Install the below packages:

1. Microsoft.SharepointOnline.CSOM 
2. Newtonsoft.Json
3. System.IdentityModel.Token.Jwt 

 

Step 3 - Add Authentication Manager Class to generate the access token

 

This class helps us to generate access tokens based on application URI, UserName, Password & Azurre AD App Client ID.

 

Create Auth Manager Class and Copy paste the below codebase:

public class AuthManager : IDisposable
   {
       private static readonly HttpClient httpClient = new HttpClient();
       private const string tokenEndpoint = "https://login.microsoftonline.com/common/oauth2/token";
       // Replace with Azure AD Client ID  -Generated in above Steps
       private const string defaultAADAppId = "Azure Active Director Client ID";

       // Token cache handling
       private static readonly SemaphoreSlim semaphoreSlimTokens = new SemaphoreSlim(1);
       private AutoResetEvent tokenResetEvent = null;
       private readonly ConcurrentDictionary<string, string> tokenCache = new ConcurrentDictionary<string, string>();
       private bool disposedValue;

       internal class TokenWaitInfo
       {
           public RegisteredWaitHandle Handle = null;
       }

       public ClientContext GetContext(Uri web, string userPrincipalName, SecureString userPassword)
       {
           var context = new ClientContext(web);

           context.ExecutingWebRequest += (sender, e) =>
           {
               string accessToken = EnsureAccessTokenAsync(new Uri($"{web.Scheme}://{web.DnsSafeHost}"), userPrincipalName, new System.Net.NetworkCredential(string.Empty, userPassword).Password).GetAwaiter().GetResult();
               e.WebRequestExecutor.RequestHeaders["Authorization"] = "Bearer " + accessToken;
           };

           return context;
       }


       public async Task<string> EnsureAccessTokenAsync(Uri resourceUri, string userPrincipalName, string userPassword)
       {
           string accessTokenFromCache = TokenFromCache(resourceUri, tokenCache);
           if (accessTokenFromCache == null)
           {
               await semaphoreSlimTokens.WaitAsync().ConfigureAwait(false);
               try
               {
                   // No async methods are allowed in a lock section
                   string accessToken = await AcquireTokenAsync(resourceUri, userPrincipalName, userPassword).ConfigureAwait(false);
                   Console.WriteLine($"Successfully requested new access token resource {resourceUri.DnsSafeHost} for user {userPrincipalName}");
                   AddTokenToCache(resourceUri, tokenCache, accessToken);

                   // Register a thread to invalidate the access token once's it's expired
                   tokenResetEvent = new AutoResetEvent(false);
                   TokenWaitInfo wi = new TokenWaitInfo();
                   wi.Handle = ThreadPool.RegisterWaitForSingleObject(
                       tokenResetEvent,
                       async (state, timedOut) =>
                       {
                           if (!timedOut)
                           {
                               TokenWaitInfo internalWaitToken = (TokenWaitInfo)state;
                               if (internalWaitToken.Handle != null)
                               {
                                   internalWaitToken.Handle.Unregister(null);
                               }
                           }
                           else
                           {
                               try
                               {
                                   // Take a lock to ensure no other threads are updating the SharePoint Access token at this time
                                   await semaphoreSlimTokens.WaitAsync().ConfigureAwait(false);
                                   RemoveTokenFromCache(resourceUri, tokenCache);
                                   Console.WriteLine($"Cached token for resource {resourceUri.DnsSafeHost} and user {userPrincipalName} expired");
                               }
                               catch (Exception ex)
                               {
                                   Console.WriteLine($"Something went wrong during cache token invalidation: {ex.Message}");
                                   RemoveTokenFromCache(resourceUri, tokenCache);
                               }
                               finally
                               {
                                   semaphoreSlimTokens.Release();
                               }
                           }
                       },
                       wi,
                       (uint)CalculateThreadSleep(accessToken).TotalMilliseconds,
                       true
                   );

                   return accessToken;

               }
               finally
               {
                   semaphoreSlimTokens.Release();
               }
           }
           else
           {
               Console.WriteLine($"Returning token from cache for resource {resourceUri.DnsSafeHost} and user {userPrincipalName}");
               return accessTokenFromCache;
           }
       }

       public async Task<string> AcquireTokenAsync(Uri resourceUri, string username, string password)
       {
           string resource = $"{resourceUri.Scheme}://{resourceUri.DnsSafeHost}";

           var clientId = defaultAADAppId;
           var body = $"resource={resource}&client_id={clientId}&grant_type=password&username={HttpUtility.UrlEncode(username)}&password={HttpUtility.UrlEncode(password)}";
           using (var stringContent = new StringContent(body, Encoding.UTF8, "application/x-www-form-urlencoded"))
           {

               var result = await httpClient.PostAsync(tokenEndpoint, stringContent).ContinueWith((response) =>
               {
                   return response.Result.Content.ReadAsStringAsync().Result;
               }).ConfigureAwait(false);

               var tokenResult = JsonSerializer.Deserialize<JsonElement>(result);
               var token = tokenResult.GetProperty("access_token").GetString();
               return token;
           }
       }

       private static string TokenFromCache(Uri web, ConcurrentDictionary<string, string> tokenCache)
       {
           if (tokenCache.TryGetValue(web.DnsSafeHost, out string accessToken))
           {
               return accessToken;
           }

           return null;
       }

       private static void AddTokenToCache(Uri web, ConcurrentDictionary<string, string> tokenCache, string newAccessToken)
       {
           if (tokenCache.TryGetValue(web.DnsSafeHost, out string currentAccessToken))
           {
               tokenCache.TryUpdate(web.DnsSafeHost, newAccessToken, currentAccessToken);
           }
           else
           {
               tokenCache.TryAdd(web.DnsSafeHost, newAccessToken);
           }
       }

       private static void RemoveTokenFromCache(Uri web, ConcurrentDictionary<string, string> tokenCache)
       {
           tokenCache.TryRemove(web.DnsSafeHost, out string currentAccessToken);
       }

       private static TimeSpan CalculateThreadSleep(string accessToken)
       {
           var token = new System.IdentityModel.Tokens.Jwt.JwtSecurityToken(accessToken);
           var lease = GetAccessTokenLease(token.ValidTo);
           lease = TimeSpan.FromSeconds(lease.TotalSeconds - TimeSpan.FromMinutes(5).TotalSeconds > 0 ? lease.TotalSeconds - TimeSpan.FromMinutes(5).TotalSeconds : lease.TotalSeconds);
           return lease;
       }

       private static TimeSpan GetAccessTokenLease(DateTime expiresOn)
       {
           DateTime now = DateTime.UtcNow;
           DateTime expires = expiresOn.Kind == DateTimeKind.Utc ? expiresOn : TimeZoneInfo.ConvertTimeToUtc(expiresOn);
           TimeSpan lease = expires - now;
           return lease;
       }

       protected virtual void Dispose(bool disposing)
       {
           if (!disposedValue)
           {
               if (disposing)
               {
                   if (tokenResetEvent != null)
                   {
                       tokenResetEvent.Set();
                       tokenResetEvent.Dispose();
                   }
               }

               disposedValue = true;
           }
       }

       public void Dispose()
       {
           // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
           Dispose(disposing: true);
           GC.SuppressFinalize(this);
       }

   }

Step 4 - Get Access Token & access SharePoint Online List data

 

 Get List Data function get data from SharePoint online List and Print out all result based on return data.

static void Main(string[] args)
      {
          List<Data> getdata = GetListData();
          foreach (Data data in getdata)
          {
              Console.WriteLine("Employee Name " + data.Title);
          }
          Console.ReadLine();
      }

The codebase will invoke the SharePoint online api with help of an access token 

public static List<Data> GetListData()
       {
           const string DataColumn = "ID,Title";
           const string DataAPIAllData = "{0}/_api/lists/getbytitle('{1}')/items?$top=10&$select=" + DataColumn + "&$orderby=Modified desc";

           try
           {
               var results = new List<Data>();

               string sharepointSiteUrl = Convert.ToString("https://mittal1201.sharepoint.com/sites/CommSiteHub");
               if (!string.IsNullOrEmpty(sharepointSiteUrl))
               {
                   string listname = "Employee";
                   string api = string.Format(DataAPIAllData, sharepointSiteUrl, listname);
                   if (!string.IsNullOrEmpty(listname))
                   {
                       //Invoke REST Call
                       string response = TokenHelper.GetAPIResponse(api);
                       if (!String.IsNullOrEmpty(response))
                       {
                           JObject jobj = Utility.Deserialize(response);
                           JArray jarr = (JArray)jobj["d"]["results"];

                           //Write Response to Output
                           foreach (JObject j in jarr)
                           {
                               Data data = new Data();
                               data.Title = Convert.ToString(j["Title"]);

                               results.Add(data);
                           }
                       }
                       return results;
                   }
                   else
                   {
                       throw new Exception("Custom Message");
                   }
               }
               else
               {
                   throw new Exception("Custom Message");
               }
           }
           catch (Exception ex)
           {
               throw new Exception("Custom Message");
           }
       }
   }

Created a data class  with filed title here

public class Data
{
public string Title { get; set; }
}

Create TokenHelper class to get access token based on user credentials and URI. This function helps to get access from AuthManager Class with the provided information.

public static string GetAPIResponse(string url)
       {
           string response = String.Empty;
           try
           {
               //Call to get AccessToken
               string accessToken = GetSharePointAccessToken();
               //Call to get the REST API response from Sharepoint
               System.Net.HttpWebRequest endpointRequest = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url);
               endpointRequest.Method = "GET";
               endpointRequest.Accept = "application/json;odata=verbose";
               endpointRequest.Headers.Add("Authorization", "Bearer " + accessToken);
               System.Net.WebResponse webResponse = endpointRequest.GetResponse();
               Stream webStream = webResponse.GetResponseStream();
               StreamReader responseReader = new StreamReader(webStream);
               response = responseReader.ReadToEnd();
               return response;
           }
           catch (Exception ex)
           {
               throw;
           }

       }

       public static string GetSharePointAccessToken()
       {

           Uri site = new Uri("https://mittal1201.sharepoint.com/sites/CommSiteHub");
           string user = "user email address";
           string pwd = "user password";
           string result;
           using (var authenticationManager = new AuthManager())
           {
               string accessTokenSP = authenticationManager.AcquireTokenAsync(site, user, pwd).Result;
               result = accessTokenSP;
           }
           return result;
       }

Output Window 

 

Execute this solution or press F5.

 

SharePoint List Screen Shot where data is going to read by a console app

 

 

Console Output

 

 

Finally, we got output using .NetCore 3.1 console app instead of .NetStandard framework. 

 

I hope you enjoyed and learned something new in this article.