Troubleshooting 'Access Denied' Errors For Sharepoint Rest Apis

Common Causes of “Access Denied” Errors

When making requests to the SharePoint REST APIs, one of the most common errors developers and IT professionals encounter is the “Access Denied” response. This indicates that the user or application attempting to perform the operation does not have the required permissions and scopes to carry it out successfully. There are a few key reasons you may receive “Access Denied” errors when working with SharePoint REST APIs:

Invalid permissions or scopes for the user or app making the request
Trying to access a site, list, or item the user doesn’t have access to
Issues with authentication or expired access tokens

The SharePoint REST interface relies heavily on permissions and OAuth authentication to regulate access to resources. If the requesting user, application, or access token don’t have the right scopes and access privileges, the API will refuse to complete the operation and return an “Access Denied” error response instead. To successfully troubleshoot these kinds of issues, you first need to understand the exact error message you are receiving.

Determining the Exact Error Message

When you make a call to a SharePoint REST endpoint and receive “Access Denied” errors, the first troubleshooting step is to inspect the full error response body, not just the HTTP status code. SharePoint REST APIs will return detailed messages that give you clues about the potential cause of the permission issue. For example, you may see errors like “The security validation for this page is invalid” or “The user does not have access to this resource.”

Table of Contents

Pay close attention to the wording used in the error message, as terms like “this action”, “this resource” or “this user” can help narrow down where the problem is rooted. Generic HTTP 403 status codes without additional error detail make the issue harder to isolate. Enable full error messaging on the API responses in your code to see the specifics. Errors referencing permissions and scopes specifically indicate a problem with assigned rights. Phrases like “cannot perform this action” strongly signal the app, user, or token don’t have correct permissions.

Viewing Error Responses in Code

When calling SharePoint REST APIs from languages like JavaScript, C#, Java, or Python, you can directly access the error response content to view these detailed messages. For example, in Node.js:

request.get({url: "/sites/mysite/_api/web/lists"}, (err, response) => {
  if (err || response.statusCode !== 200) {
    console.log(response.body); // View error message from response
  }
});

Pay attention to the body of erroneous responses which call out permission issues. By default, many client libraries may only show you status codes, so make sure full error bodies are exposed.

Validating Permissions and Scopes

Once you have determined the generalized cause – permissions, access rights, or scopes – based on the error messaging, you can start validating that the user or application has the required privileges to perform the operation in question. Almost all functions against the SharePoint REST API require specific permissions, beyond just general access to the SharePoint environment. For example, the ability to create lists and post items requires “Sites.ReadWrite.All” scopes.

Double check that the user or application has been granted the appropriate permissions against the SharePoint site collection to carry out the operation. Use the SharePoint admin interfaces or PowerShell to verify assigned permissions. You can also programatically check scopes and rights using REST queries against the user and site endpoints. For example:

  
GET /sites/dev/_api/web/effectivebasepermissions
GET /sites/dev/_api/web/lists/getbytitle('Contacts')/EffectiveBasePermissions

Here you can see the collection of permissions exposed at the site level versus permission levels granular to a specific list. Try removing different scope grants to determine the minimally required set of access privileges needed. As a general rule, use the most restrictive set of permissions and scopes possible that enable your target goal.

Validating OAuth Scopes

When connecting to SharePoint REST interfaces via registered OAuth apps, pay close attention to requested scopes during the authentication process. For example, a Microsoft Graph application might request:

SCOPES = ['Sites.ReadWrite.All', 'User.ReadWrite.All']

Then when calling the Graph API to create a SharePoint list, an “Access Denied” error is thrown because the Graph scopes do not overlap with the granular SharePoint permissions. Adjust scopes to include permissions like:

  
SCOPES = ['Sites.ReadWrite.All', 'TermStore.ReadWrite.All']

Ensure any custom-registered apps are requesting scopes closely aligned to their functional goals. You cannot broadly assume a given predefined permission set will cover every contemplated API operation.

Checking Site, List, and Item Access

Beyond validating technical permissions and scopes, also verify the user or application has business access to the specific SharePoint sites, lists, libraries, and items they are attempting to interact with via the REST APIs. An “Access Denied” error when making a POST request to add a new item might simply indicate the user does not have write access to the target list itself. They could have broad permissions but still be blocked from certain containers or leaf nodes.

Manually check if the user can access the SharePoint site directly through the browser interface and perform the operations being attempted through the API. If direct UI access is blocked while using proper credentials, then the REST calls will often fail the same way. Revoke and re-grant access at site, list, library, or item granularity until the specific blocked resource is identified.

Examine the permission inheritance model in the site hierarchy to determine where access is first denied. For example, if user A cannot access documents in folder B, check the permissions set on the parent site, the specific library hosting the folder, as well as individual folder settings. Identify where read/write access first disappears as you go down the inheritance tree.

Checking Recent Permission Changes

Also verify if permission changes were recently applied that may have revoked previous access the user or app had. Certain operations against the SharePoint REST APIs may have been working previously, but sudden permission configuration changes could now trigger “Access Denied” errors where none occurred before. Check any permission changes within a relevant timeframe of when the errors began occurring – seeing if that lines up with lost access.

Troubleshooting Authentication Issues

Invalid or expired authentication credentials are another common source of “Access Denied” problems with SharePoint REST APIs. SharePoint uses OAuth 2.0 and access tokens for securing API authentication, issuing time-bound tokens that eventually expire. At that point calls fail due to invalid credentials. You need to re-authenticate and acquire fresh tokens.

Verifying Access Token Validity

Check if the access tokens you are using have expired. Typically these expire within the hour. The exact expiration time can be seen decoded within the token itself. Base64 decode the access token and inspect exp or nbf claims. You can quickly decode tokens using an online JWT decoder. If the current time is past the listed exp claim, you need to generate a new access token.

Requesting Fresh Access Tokens

Refreshing request access tokens involves re-authenticating with the SharePoint OAuth 2.0 authentication endpoints. You supply your original refresh token, client ID, and client secret to generate fresh short-lived access tokens. Save the new access tokens and use them in subsequent API calls. Below shows an example using the OAuth2 authorization code grant flow:

// Initial auth redirect and get authorization code 

var tokenUrl = `https://accounts.accesscontrol.windows.net/${tenantId}/tokens/OAuth/2`;  

var body = {
  grant_type: "refresh_token",
  refresh_token: "ORIGINAL_REFRESH_TOKEN", 
  client_id: "CLIENT_ID",
  client_secret: "CLIENT_SECRET",
  resource: "00000003-0000-0ff1-ce00-000000000000/contoso.sharepoint.com@f70eab96-2541-41eb-b0b3-171a81fdd34a"
}

fetch(tokenUrl, {
  method: 'POST',
  body: QueryString.stringify(body)
}).then(response => {
  return response.json(); 
}).then(tokenResponse => {

  // Refresh tokens successful 
  // Use new access tokens in API calls  

});

Be sure to use the latest access token issuances in SharePoint requests, discarding any cached tokens that may have expired.

Validating with OAuth Playground

To test authentication and eliminate doubts around access token validity, walk through permissions using the Office 365 OAuth Playground site: https://developer.microsoft.com/en-us/microsoft-365/dev-program. This site prompts you through login OAuth flows for acquiring test tokens using custom registered apps.

Supply these tokens to directly issue REST calls against SharePoint to prove viability. The playground eliminates concerns around proper token issuance compared to custom authentication code you may have implemented.

Example Code for Common REST Operations

With authentication issues eliminated from consideration, see code examples for issuing basic CRUD operations against SharePoint lists and libraries below. The examples handle proper OAuth token retrieval, HTTP requests, response handling, and permission passing. Adapt these samples to your specific site URLs, list names, etc.

Creating a Custom List

// Get access token
var accessToken = "eyJ0eXAiOiJKV1Q...9m7Xp_mgltc"; 

// Build List Creation Payload
var listCreation = {
  "allowContentTypes": true, 
  "baseTemplate": 100,   
  "contentTypesEnabled": true,
  "description": "My custom list",
  "title": "TestList"
};

// Create List REST Request
fetch('/sites/dev/_api/web/lists', {
  method: 'POST',
  body: JSON.stringify(listCreation),
  headers: {
    "Authorization": `Bearer ${accessToken}`, 
    "Content-type": "application/json" 
  }  
}).then(response => {

  // Check response status
  if(response.status === 201) {
    console.log("List created successfully!");
  } else { 
    // Handle errors
  }  
});

Adding List Items

// Build list item payload
var itemProperties = {
  "Title": "New Document",
  "DocumentType": "Specification",
  "DocumentStatus": "Draft"  
};

// POST request to add item 
fetch('/sites/dev/_api/web/lists/getbytitle('Documents')/items', {
    method: 'POST',
    body: JSON.stringify(itemProperties),
    headers: {
      "Authorization": `Bearer ${accessToken}` 
    }
}).then(response => {
  
  // Check response
  if(response.status === 201) {
    console.log("Item added");
  }

});

Be sure to pass valid OAuth tokens with necessary permission scopes in any request. The examples above would require read/write permissions on the site and target list. Capture and inspect responses to diagnose errors.

Additional Troubleshooting Tips

With “Access Denied” issues, some additional things to check include analyzing more detailed logs, capturing network traces, and eliminating custom code defects.

Reviewing ULS Logs

The SharePoint Unified Logging Service (ULS) logs record detailed diagnostics around API operations which you can inspect to troubleshoot permission errors. Administrators can collect and filter ULS logs around the timestamps of denied API calls to see extended error information. ULS entries may contain denied stack traces unavailable in request responses. Enable verbose ULS logging for your API requests when testing.

Capturing Network Traces

Use network tracing tools like Fiddler to capture the full HTTP traffic between your code and SharePoint when calling the REST APIs. Inspect request and response bodies, headers, returned status codes. Compare trace logs from a successful vs access denied request to pinpoint differences such as invalid tokens or scope issues. The network traces contain API communication details unavailable through code alone.

Checking Custom Code Defects

If interfacing with the SharePoint REST API through custom application code, ensure there are no defects occurring in your implementation preventing valid permissions from being passed. For example, a JavaScript bug could be sending an empty bearer token instead of a properly populated access token in the request Authorization header. Carefully debug code to eliminate these kinds of defects that could prevent valid authentication parameters from reaching SharePoint APIs.

Troubleshooting ‘Access Denied’ Errors For Sharepoint Rest Apis