How to access SharePoint Online data using Postman - REST API and Bearer token


You can interact with SharePoint via REST API's and perform actions like adding, deleting, updating, fetching data. Two popular approaches are using SharePoint App Registration and Azure AD app (Graph API).

As a developer you are required to build the correct REST query for use, or may be even pass on to another developer (OAuth + REST) for consuming in 3rd party external platforms like Java, Python, .Net, etc. It is a good idea to test the links before use.
Another important factor is Authentication and Authorization while accessing SharePoint information, you may want to use the app credentials (client Id and Secret) and confirm connectivity.

⭐ Postman

Postman is a great tool used for HTTP API testing, where REST API can be used to retrieve, add, delete, update data. You can examine the response in JSON, XML, HTML, Text format before actual development, without writing any code.
If everything looks good, you can generate code snippets in almost all language/framework like Python, PowerShell, Java, C, C#, etc. and embed it directly in your code, that's rapid development.

Read more on Postman and download here.

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We will learn how to use Postman to access SharePoint data using REST API and save time and efforts during development.

⚡️ How to test SharePoint REST API using Postman

To authorize and access SharePoint REST API from outside of SharePoint (external application), we need to generate Bearer token ("using Client Id" and "Client Secret") by registering SharePoint App and pass with request header and the URL. Refer link below for steps.

High level steps are outlined below.
  1. Register the SharePoint Add-In
  2. To begin, we need to register a SharePoint Add-In and grant it permissions to access SharePoint information, like site, document library, lists.

    Refer this article for steps - steps to register SharePoint Add-In, generate 'client id' and 'client secret', grant permissions.


  3. Retrieve the Tenant ID
  4. Now with the App registered, we are ready to access the SharePoint Online information from external system or tools.
    We will retrieve the Tenant ID of SharePoint Online tenant using Postman tool.
    • Launch the Postman client.
    • Select "Get" Method for Request (refer image below).
    • In the "Request URL" textbox, enter URL in this format.
    • FORMAT --> https://[sitename].sharepoint.com/_vti_bin/client.svc/

      EXAMPLE --> https://c2c.sharepoint.com/_vti_bin/client.svc/

    • Navigate to the Header section and add Key "Authorization" to send with the request (refer image below).
    • Headers

      Key Value
      Authorization Bearer

    • Click "Send" to submit the request.
    • Postman SharePoint 401 Unauthorized Access Denied
      Postman SharePoint 401 Unauthorized Access Denied

    • The response will fail with status message "401 Unauthorized".
    • System.UnauthorizedAccessException

      Access denied. You do not have permission to perform this action or access this resource.

    • We will generate the (access) Bearer token to fix this error.

  5. Generate the Access Token

  6. Now we will generate the bearer access token from Postman tool, which will be used to access the SharePoint information.
    • Examine the the response Header section (refer image below) and look for "WWW-Authenticate" header. Look for below 2 values and note them for future use - realm and client_id.

      realm = value for the SharePoint Online Tenant Id (varies for each M365 Tenant)

      client_id = value for resource information (this value is common always)

    • Postman SharePoint - Retrieve Tenant ID
      Postman SharePoint - Retrieve Tenant ID

    • After getting the "Tenant ID", we will request the Access Token. To do this, use URL in the below format.

      https://accounts.accesscontrol.windows.net/[Tenant ID]/tokens/OAuth/2

      [Tenant ID] = realm value from the previous step
    • Select the request as POST method.
    • Apply Header configuration parameters as below.

      Headers

      Key Value
      Content-Type application/x-www-form-urlencoded

      Postman SharePoint - Generate Token Headers
      Postman SharePoint - Generate Token Headers

    • Apply Body configuration parameters as below.

      Body

      Key Value
      grant_type client_credentials
      client_id ClientID@TenantID
      client_secret ClientSecret (generated while App registration)
      resource resource/SiteDomain@TenantID

      You will need to build some values by combining multiple values fetched previously.

      client_credentials = client_credentials (use as it, do not change)

      ClientID@TenantID = Client ID (generated during App registration) + @ sign + Tenant ID (fetched while retrieving Tenant ID)

      ClientSecret = Client Secret generated while App registration

      resource/SiteDomain@TenantID = 00000003-0000-0ff1-ce00-000000000000 + "/" sign + c2c@sharepoint.com + @ sign + Tenant ID (fetched while retrieving Tenant ID)


      Postman SharePoint - Generate Token Body
      Postman SharePoint - Generate Token Body

    • Click Send button to submit the request.
    • The Status is now shown as "200 OK" which means the connection to SharePoint Online was successful using the client id and secret.
    • Now we can find the access token from the "Body" section (refer image below). Copy the value of parameter/key "access_token" and note for use the future steps.
    • Postman SharePoint - Generate Bearer Access Token
      Postman SharePoint - Generate Bearer Access Token

    • Important Note - The (access) Bearer token has an expiry and is valid only for few hours (5 to 6 hours usually). So you need to generate the new token regularly via your code.


  7. Access the SharePoint resource (list, library, site, listitem, documents, etc.)
  8. With the access token secured, the REST query will be authorized to access SharePoint data depending on the permission granted via the Add-In.
    • Now, let us connect and access SharePoint Online using Postman. Use a very simple REST query to fetch the SharePoint Online site Title (replace URL to your own SharePoint site to which the App has access).

      https://c2c.sharepoint.com/_api/web?$select=Title

    • Select the request as GET method.
    • Apply Header configuration parameters as below.

      Headers

      Key Value
      Authorization Bearer [value of access_token]
      Accept application/json;odata=verbose

      Note that there is a space in between Bearer and Access token value (refer image below).

    • Click the "Send" button
    • Postman SharePoint - REST test
      Postman SharePoint - REST test

    • Response should be success with status 200 OK and the SharePoint Online site Title should be returned (Body section), assuming all values were passed correctly. If there is an access denied or unauthorized access error, check the configuration again.
      You can examine the response in JSON, HTML, plain text, etc.


  9. More testing
  10. You can use various REST API queries with GET (read), POST (create), PUT (update), PATCH (partial update) methods and try performing different operations like -
    • Read SharePoint information - List items, Documents, etc.
    • Write to SharePoint - create lists, create list items, upload documents, etc.
    • Fetch search results - using search API's.
    • Try Graph API.
    • Other more ways to explore.

⚡️ Generate code snippets form Postman

You can generate code snippets in various languages and frameworks with Postman. Select the request --> click Code icon (right panel) --> select language --> view and copy generated code snippet.
These code snippets are ready-to-use, just embed them in your code and start using (ensure you pass in correct authorization account/key for connection).


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