Get Access token for update list item using REST API and JavaScript application

Question

I need to update an item on a list using REST API and JavaScript application from this site I try to use this code:

url: http://site url/_api/web/lists/GetByTitle(‘Test')/items(item id)
method: POST
body: { '__metadata': { 'type': 'SP.Data.TestListItem' }, 'Title': 'TestUpdated'}
headers:
     Authorization: "Bearer " + accessToken
     X-RequestDigest: form digest value
    "IF-MATCH": etag or "*"
    "X-HTTP-Method":"MERGE",
    accept: "application/json;odata=verbose"
    content-type: "application/json;odata=verbose"
    content-length:length of post body

but I don't know how to get accessToken and without Authorization header I can't use this request (I get 401 Unauthorized error). So how can I get this access token?

Answer 1

You have to pass TenantID, Client ID, Client Secret and resource details to get the access token.

First of all, To get the Tenant ID; we have to navigate to below URL, https://.sharepoint.com/_vti_bin/client.svc/ . This will return the tenant ID.

Then, use the below script to get the access token,

$.ajax({
    type: 'POST',
    crossDomain: true,
    url: 'https://cors-anywhere.herokuapp.com/https://accounts.accesscontrol.windows.net/<tenantID>/tokens/OAuth/2',
    headers: {
        "content-type": "application/x-www-form-urlencoded"
    },
    data: {
        "grant_type": "client_credentials",
        "client_id": "<ClientID>@<TenantID>",
        "client_secret": "<ClientSecret>",
        "resource": "00000003-0000-0ff1-ce00-000000000000/<sitename>.sharepoint.com@<TenantID>"
    },
    success: function(data) {
        //data.token_type returns "Bearer"
        //data.access_token returns < AccessToken >
        var at = data.token_type + " " + data.access_token;
      //caal the REST API with the at variable in header

    },
    error: function(data, errorThrown, status) {

    }
});

//To get the access token from the ajax, we have to use some proxy file. In the above example code, we have used https://cors-anywhere.herokuapp.com as a proxy file.
//If we try to get the access token in same domain, we don't need to use https://cors-anywhere.herokuapp.com

Please check the below link, which helps you to get the access token using Postman tool, http://www.ktskumar.com/2017/01/access-sharepoint-online-using-postman/