Testing Coinbase API with Postman : pagination gives me error - api

Question

I am testing the Coinbase API endpoints with Postman and the challenge is when I need to paginate
In order to setup Postman, I have followed the guide available here and in summary:
added variables
coinbase-api-base
coinbase-api-key
coinbase-api-secret
coinbase-api-timestamp
coinbase-api-signature
Added pre-request script in order to generate the request signature
// 1. Import crypto-js library
var CryptoJS = require("crypto-js");
// 2. Create the JSON request object var req = { timestamp: Math.floor(Date.now() / 1000), // seconds since Unix epoch method:
pm.request.method, path: pm.request.url.getPath(), body: '', // empty
for GET requests message: undefined, secret:
pm.collectionVariables.get("coinbase-api-secret"), // read value from
collection variable hmac: undefined, signature: undefined, };
// 3. Create the message to be signed req.message = req.timestamp + req.method + req.path + req.body;
// 4. Create HMAC using message and API secret req.hmac = CryptoJS.HmacSHA256(req.message, req.secret);
// 5. Obtain signature by converting HMAC to hexadecimal String req.signature = req.hmac.toString(CryptoJS.enc.Hex);
// 6. Log the request console.info("request: ", req);
// 7. Set Postman request's authentication headers for Coinbase REST API call pm.collectionVariables.set("coinbase-api-timestamp",
req.timestamp); pm.collectionVariables.set("coinbase-api-signature",
req.signature);
all worked well for a simple request such as:
GET {{coinbase-api-base}}/v2/accounts
then, if I add in the body request parameter (as explained here):
limit=50
to change the default pagination, I get an authentication error....
"errors": [
{ "id": "authentication_error",
"message": "invalid signature"
}
questions:
how can I fix it?
how the body of the request can play with the request signature...
any help suggestion is much appreciated
Thank you

Answer 1

Edit: the below being said, I'm not sure the base accounts API supports paging I could be wrong though, the CB docs are inconsistent to say the least. It does seem that the account history (ledger) and holds do though.
https://docs.cloud.coinbase.com/exchange/reference/exchangerestapi_getaccounts
get accounts function in Node.js API doesn't give an args param where the ledger does (see below):
getAccounts(callback) {
return this.get(['accounts'], callback);
}
Documentation for an api that does support paging, notice it gives you a query param section not available in the accounts documentation:
https://docs.cloud.coinbase.com/exchange/reference/exchangerestapi_getaccountledger
Looking at the node api, you still need to add the query string params to the body in order to sign:
calling function:
return this.get(
['accounts', accountID, 'ledger'],
{ qs: args },
callback
);
signing function:
let body = '';
if (options.body) {
body = JSON.stringify(options.body);
} else if (options.qs && Object.keys(options.qs).length !== 0) {
body = '?' + querystring.stringify(options.qs);
}
const what = timestamp + method.toUpperCase() + path + body;
const key = Buffer.from(auth.secret, 'base64');
const hmac = crypto.createHmac('sha256', key);
const signature = hmac.update(what).digest('base64');
return {
key: auth.key,
signature: signature,
timestamp: timestamp,
passphrase: auth.passphrase,
};

Answer 2

You can't add the limit to the body of the request, GET requests never includes any body.
You should add it as a query string parameter like (this is just an example):
GET {{coinbase-api-base}}/v2/accounts?limit=50