Resolving Postman Authentication Issues When Accessing Sharepoint Online Rest Apis

Understanding Authentication Requirements

SharePoint Online utilizes OAuth 2.0 authentication protocols to authorize client applications access to its REST APIs. Successful OAuth implementation requires configuring POSTMAN to meet SharePoint Online’s specific authentication requirements.

The SharePoint REST APIs require authenticated access using Azure Active Directory OAuth bearer tokens. Developers must register POSTMAN as an Azure AD application to receive the required OAuth credentials for generating access tokens. Configuration steps include registering a POSTMAN app, granting API permissions, and retrieving the client ID and client secret.

Once POSTMAN contains the necessary OAuth app identity, authentication requests can be constructed to exchange the client ID and secret for access tokens. Tokens permit short-term authorized interaction with SharePoint through its REST endpoint URLs. However, tokens eventually expire and must be refreshed to maintain ongoing API access.

Common Access Scenarios

Typical SharePoint API access scenarios from POSTMAN include:

• File management – Create, read, update, delete SharePoint documents.
• List management – Query, add, edit, remove SharePoint lists and list items.
• Search – Execute search queries against SharePoint content and metadata.
• User profiles – Read and modify SharePoint user attributes and data.

OAuth Token Characteristics

When accessing the SharePoint REST APIs, developers should understand important OAuth token traits:

• Short-lived – Tokens are only valid for a limited period before expiring. Typical validity is 1 hour.
• Renewable – New tokens can be generated to continue access by using refresh tokens.
• Revocable – Auth servers can invalidate tokens forcing re-authentication.
• Bearer tokens – Simple string tokens pass in request headers.
• Scopes – Tokens specify authorized scopes like user profile, files, sites, etc.

Configuring Postman for SharePoint Online Access

Registering an Azure AD POSTMAN Application

An Azure AD app registration must be created for POSTMAN to integrate authentication capabilities. Navigate to the Azure Active Directory Admin Center and register a new application.

1. Select Azure Active Directory > App registrations > New registration.
2. Provide an application Name and Supported account types.
3. Under Redirect URI, specify the POSTMAN OAuth URL https://www.getpostman.com/oauth2/callback.
4. Once created, the Application (client) ID will be displayed. Copy this for later OAuth client configuration in POSTMAN.

Adding API Permissions

The Azure AD app requires declared permissions to access SharePoint APIs. Under API permissions, add access for:

• Microsoft Graph – For general SharePoint Online permissions.
• SharePoint Service – For SharePoint document/file permissions.

Select the Delegated permissions checkboxes desired for API access levels.

Retrieving the Client Secret

The OAuth authentication flow requires the POSTMAN app’s client secret. Under Certificates & secrets:

1. Select New client secret.
2. Provide a Description and select an Expires timeframe.
3. The app secret value will then be displayed. Copy this immediately as it cannot be retrieved afterwards.

OAuth Configuration Settings in POSTMAN

With the Azure AD app credentials gathered, the POSTMAN client can now be configured for OAuth 2.0 capabilities:

1. Select the gear icon > Authorization to access OAuth settings.
2. Choose OAuth 2.0 as the authorization type.
3. Enter the copied Azure AD Client ID and Client Secret.
4. Specify the Auth URL https://login.microsoftonline.com/common/oauth2/v2.0/authorize
5. Provide the Access Token URL https://login.microsoftonline.com/common/oauth2/v2.0/token
6. Select an appropriate Scope for SharePoint API access permissions.
7. Enable Request Access Token Locally.

POSTMAN is now integrated with Azure AD OAuth APIs to request access tokens granting access to SharePoint Online.

Obtaining Access Tokens

The OAuth Authentication Flow

With OAuth properly configured, POSTMAN can obtain access tokens permitting API interaction. The key authentication steps include:

1. Initial authorization request to Azure AD asking for a token – Includes OAuth client ID and requested scopes.
2. Azure AD consent page allowing the app’s API access to account data based on scopes.
3. Redirect back to POSTMAN’s callback URL with an authorization code.
4. Exchanging authorization code for an access token permitting authorized API requests – Uses client ID and secret.

Constructing the Token Request

With OAuth configured, POSTMAN requests access tokens using:

1. Select the Authorization tab to view OAuth settings
2. Choose the configured SharePoint Scope matching the API permissions desired.
3. Select Request Token to initiate the OAuth token-generation flow.
4. If prompted, provide Azure AD login credentials permitting consent.

If successful, an OAuth access token will be embedded into POSTMAN for subsequent API requests. The token permits exactly the scopes consented to.

Using the Access Token

Once obtained, access tokens are automatically attached to SharePoint REST API requests made from POSTMAN.

For example, requesting a site’s root REST endpoint would include the header:

Authorization: Bearer {token}

All responses to REST requests will reflect the access permissions consented in the authenticated token scopes.

Refreshing Expired Tokens

Determining Token Expiration

Access tokens have limited lifetimes before expiring – typically 1 hour. Once expired, calls to SharePoint APIs will return authorization errors instead of requested data.

The token expiration period can be confirmed by decoding the token string and reviewing the exp property.

Using Refresh Tokens to Renew Access

To avoid re-prompting the user to consent permissions, POSTMAN uses refresh tokens to seamlessly obtain new access tokens after expiration:

1. A refresh token allowing new access tokens is provided alongside the initial access token.
2. Before expiration, POSTMAN automatically refreshes the access token using the refresh token.
3. The process continues perpetually unless token revocation or scope change occurs.

This refresh approach prevents authorization flow interruptions when accessing APIs long-term.

Re-Prompting User Consent

Despite refresh capabilities, certain scenarios still require user interaction to obtain new tokens:

• Adding/changing requested scopes requires re-consent.
• Token revocation by admin forces new consent.
• The POSTMAN app’s access being disabled in Azure AD.

Handling these consent & authorization interruptions requires developer attention, especially in production systems.

Troubleshooting Common Authentication Errors

Even with proper OAuth configuration, access token requests can fail. Common errors include:

Invalid or Incorrect Scopes

If the token request declares scopes not consented to in Azure AD, an invalid_scope error will occur preventing token generation.

Resolution: Re-check the SharePoint API permissions enabled in the app registration settings match the scopes declared in your POSTMAN requests.

Authorization Code Redirect Mismatch

A mismatch between the configured callback URL and the OAuth redirect attempt returns an authorization error.

Resolution: Confirm POSTMAN’s OAuth settings utilize the exact redirect URL registered in the Azure AD application.

Expired Tokens

Once access tokens expire after the configured period, subsequent API calls fail authorization.

Resolution: Configure POSTMAN to automatically refresh tokens using refresh tokens to avoid interruptions.

Revoked OAuth App Registration

Administrators can revoke the OAuth application registration blocking authentication capabilities.

Resolution: The POSTMAN app registration must be re-enabled in Azure AD to restore OAuth capabilities.

Example API Calls with Postman

Constructing SharePoint REST Endpoints

With access tokens obtained, POSTMAN can directly interact with SharePoint REST resources. Endpoints follow the format:

https://[tenant_name].sharepoint.com/_api/[service]/[entity] 

Common elements include:

• Tenant_name – The SharePoint tenant or domain accessed.
• Service – The API category like sites, web, lists, userprofiles, search, etc.
• Entity – The specific SharePoint object or resource.

For example, requesting list items from the Contacts list:

 
https://tenant.sharepoint.com/_api/web/lists/getbytitle('Contacts')/items

Common POSTMAN API Tasks

Interacting with SharePoint data via REST APIs from POSTMAN involves requests like:

• GET – Query and retrieve SharePoint entities and metadata.
• POST – Create new objects like files, folders, list items, etc.
• PUT – Update existing SharePoint objects.
• DELETE – Remove existing SharePoint resources.

Constructing the HTTP requests properly is essential for successful API access.

Sample POSTMAN Collection

A pre-built POSTMAN collection helps jumpstart SharePoint API interactions including:

• Site metadata requests
• List and list item queries
• Add, edit, and remove documents
• Manipulate Microsoft Graph user profiles

Import this collection for pre-fabricated calls after configuring OAuth credentials.