Access Google spreadsheet API without auth token

It is possible to write to spreadsheet without OAuth or API Keys. You need to use Service Account Keys.

Here is what I did for my Node.js environment.

1. Get a service account key from https://console.cloud.google.com/apis/credentials (You can here also restrict what this keys is allowed todo)
   1. When creating, make sure you click the Furnish a new private key
   2. Select JSON when it asks you how to download the key.
2. The service account key you have just generated includes a client_email.
   1. Go to you google spreadsheet and allow this client_email to have write access on this document

3. Use the following code to authenticate

   let jwtClient = new google.auth.JWT(client_email, null, private_key, [ "https://www.googleapis.com/auth/spreadsheets", ]); //authenticate request jwtClient.authorize(function(err, tokens) { // at this point the authentication is done you can now use `jwtClient` // to read or write to the spreadsheet });

client_email and private_key are part of the service account key

A more detailed description can be found here. http://isd-soft.com/tech_blog/accessing-google-apis-using-service-account-node-js/ Also, all credit goes to this page.

Finally digged deep enough and found the answer. Any kind of writing, even to publicly editable sheets requires an OAuth flow:

https://issuetracker.google.com/issues/36755576#comment3

Jürgen Brandstetter's answer above is completely right. Using Postman, I have been successful without using an OAuth token (I needed my personal API key and a service account) - I have written to a new sheet (in fact I did a batchUpdate operation with two steps, first create a new sheet and then pasteData on it). I followed the instructions here to create a service account, downloaded the credentials JSON and used it to create and sign a JWT string that is later used as Bearer.

Here is the Java code to obtain the JWT string:

    private static String getSignedJWT() throws IOException {
        InputStream in = YourClass.class.getResourceAsStream("/downloaded-service-account-creds.json");
        if (in == null) {
            throw new FileNotFoundException("Resource not found");
        }
        ServiceAccountCredentials serviceAccountCredentials = ServiceAccountCredentials.fromStream(in);
        GoogleCredentials googleCredentials = serviceAccountCredentials
                .createScoped(Collections.singletonList(SheetsScopes.SPREADSHEETS));

        PrivateKey privateKey = serviceAccountCredentials.getPrivateKey();
        String privateKeyId = serviceAccountCredentials.getPrivateKeyId();

        long now = System.currentTimeMillis();

        Algorithm algorithm = Algorithm.RSA256(null, (RSAPrivateKey)privateKey);
        String signedJwt = JWT.create()
                .withKeyId(privateKeyId)
                .withIssuer(serviceAccountCredentials.getClientEmail())
                .withSubject(serviceAccountCredentials.getClientEmail())
                .withAudience("https://sheets.googleapis.com/")
                .withIssuedAt(new Date(now))
                .withExpiresAt(new Date(now + 3600 * 1000L))
                .sign(algorithm);

        return signedJwt;
    }

Dependencies needed: com.auth0:java-jwt and com.google.auth:google-auth-library-oauth2-http.

Here's the curl that uses the JWT string generated above:

curl --location --request POST 'https://sheets.googleapis.com/v4/spreadsheets/YOUR_SHEET_ID:batchUpdate?key=ANY_PERSONAL_API_KEY' \
--header 'Accept: application/json' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer YOUR_JWT_STRING' \
--data-raw '{
    "requests": [
        {
            "addSheet": {
                "properties": {
                    "title": "newPred",
                    "sheetId": 0
                }
            }
        },
        {
            "pasteData": {
                "coordinate": {
                    "columnIndex": 0,
                    "rowIndex": 0,
                    "sheetId": 0
                },
                "delimiter": "\t",
                "data": "col1\tcol2\nPeter\t25",
                "type": "PASTE_NORMAL"
            }
        }
    ]
}'

Not exactly what asked but here is a solution with google-api-nodejs-client worked for me:

const { google } = require('googleapis');
const sheets = google.sheets('v4');
const spreadsheetId = '.........';

(async () => {

  const auth = new google.auth.GoogleAuth({
    keyFile: './my_service_account_privatekey.json',
    scopes: ['https://www.googleapis.com/auth/spreadsheets'],
  });

  // get
  try {
    const getResult = await sheets.spreadsheets.values.get({
      auth,
      spreadsheetId,
      range: 'Sheet1!B2:C4'
    })
    console.log('Got values:', getResult.data.values)
  } catch (error) {
    console.error('Get error:', error)
  }


})()

docs: https://github.com/googleapis/google-api-nodejs-client#using-the-keyfile-property