How do I interact with Coinbase's API? Why does it always fail?

Question 1

YE GREAT OAUTH TUTORIAL

<?php

/*OAuth is great. It's also complicated. Or rather, it LOOKS complicated.

This whole script is just one big long function. It's a really, really ugly
function. I broke down everything "Barney-style" to demonstrate all the steps
in the process, and because there are some things you have to decide -- how to
record the user data, for instance.

Let's get this train wreck a rollin'.*/

function oauthRequest($apiPath,$getOrPost,$parameters){

/*You get this info from https://coinbase.com/oauth/applications*/
$clientId = "#####";
$clientSecret = "#####";
$callbackUrl = "http://www.blah.com/oauth.php";

function curling($url,$getpost,$params){
    if($params != ""){
        $params = http_build_query(json_decode($params), true);
    }
    if($getpost == "get"){
        $ispost = false;
        $url .= $params;
    }
    $ch = curl_init();
    curl_setopt_array($ch, array(
        CURLOPT_URL => $url,
        CURLOPT_RETURNTRANSFER => true
    ));
    if($getpost == "post"){
        curl_setopt_array($ch, array(
            CURLOPT_POST => $ispost,
            CURLOPT_POSTFIELDS => $params
        ));
    }
    $results = curl_exec($ch);
    curl_close($ch);
    return $results;
}

/*There are two people involved here: the Client (you), and the User (the
person accessing your app or site).

You'll need 3 pieces of data for each user before your app can access their
Coinbase account: a User Code, an Access Token, and a Refresh Token.

For the purposes of this demonstration, I'm recording all of the user data in
a .txt file on my server. THIS IS PROBABLY A BAD IDEA in real life because .txt
files aren't secure at all, and this text file will only store the data for one
user (it gets overwritten every time). This is the kind of stuff you'd put in an
SQL database if you have one, or maybe in the user's cookies.*/

if(!file_exists("userdata.txt") || file_get_contents("userdata.txt") == ""){
    file_put_contents("userdata.txt",json_encode(array(
        "userCode" => "",
        "accessToken" => "",
        "refreshToken" => ""
    )), LOCK_EX);
}
$userData = json_decode(file_get_contents("userdata.txt"), true);

/*Okay. So. First thing we're going to do is see if we have a User Code for
this user. These are big alphanumeric strings that are 64 characters long. If
we have one, it'll either be in the URL of this page (the $_GET array), or
it'll be in that userdata.txt file.*/

if(array_key_exists("code",$_GET) && $_GET["code"] != ""){
    $userCode = $_GET["code"];
}else if(array_key_exists("userCode",$userData) && $userData["userCode"] != ""){
    $userCode = $userData["userCode"];
}else{

/*If we don't have a User Code, then this next snippet of code will fire. It'll
return the link for a special user-specific Coinbase page to which the user
will need to go to authorize your app to access their Coinbase account (by
signing into Coinbase and clicking a green "Authorize" button).

After authorizing your app, they'll be automatically taken to the Redirect URL
you specified, with their User Code added to the end of the URL. So if your
Redirect URL is www.blah.com/oauth.php, they'll go to www.blah.com/oauth.php?
code=123451234512345 .

This User Code never expires, and so theoretically the user should only need to
go to the authorization link once. However, if you don't make a way of getting
the User Code in the future (my fancy "userdata.txt" in this case) or they de-
authorized your app from within their Coinbase account, then they'll need to go
to the link again and re-authorize your app from the beginning.

I have it set up so my Redirect URL and the rest of my OAuth script are all on
the same page: www.blah.com/oauth.php . So the user will just start back at the
beginning of this script, and THIS time the script will see the User Code in
the URL (the $_GET array), and so will skip this next bit.

Whew. You with me so far?*/
    return ("https:/*coinbase.com/oauth/authorize?" . http_build_query(array(
        "response_type" => "code",
        "client_id" => $clientId,
        "redirect_uri" => $callbackUrl
    )));
    die;
}

/*Here I am, recording the User Code for future use in userdata.txt*/
$userData["userCode"] = $userCode;
file_put_contents("userdata.txt",json_encode($userData),LOCK_EX);

/*Alright, we've got the User Code. Now we need the Access Token -- another 64-
character string. The difference is that the Access Token expires every 2 hours
(7200 seconds). Let's see if we already have one in the userdata.txt file.*/
if(array_key_exists("accessToken",$userData) && $userData["accessToken"] != ""){
    $accessToken = $userData["accessToken"];
    $refreshToken = $userData["refreshToken"];
}else{

/*If we're here, it's because we don't have an Access Token for this user. We
get one by making this POST request:*/
    $authorization = json_decode(curling(
        "https:/*coinbase.com/oauth/token" . "?" . http_build_query(array(
            "grant_type" => "authorization_code",
            "code" => $userCode,
            "redirect_uri" => $callbackUrl,
            "client_id" => $clientId,
            "client_secret" => $clientSecret
        )), "post", ""), true);
    if(array_key_exists("error",$authorization)){

/*If something goes wrong here, I'm going to clean out userdata.txt and ask the
user to try again.*/
        file_put_contents("userdata.txt","",LOCK_EX);
        die("Something went wrong. Please refresh the page and try again.");
    }
    $accessToken = $authorization["access_token"];
    $refreshToken = $authorization["refresh_token"];
}

/*The Refresh Token is what you use to get a new Access Token once the current
Access Token has expired. The Refresh Token never expires, but can only be used
once. Anytime you get an Access Token, you'll also be given a Refresh Token.

If you don't have the Refresh Token and a working Access Token for the user,
they'll need to re-authorize your app all over again.

I'm backing up the Access Token and Refresh Token to userdata.txt*/
$userData["accessToken"] = $accessToken;
$userData["refreshToken"] = $refreshToken;
file_put_contents("userdata.txt",json_encode($userData),LOCK_EX);

/*Alright! At this point, we should have the three bits of user data we need:
the User Code, the Access Token, and the Refresh Token. So now lets try
actually making an API request.

This whole script is really just one big function called "oauthRequest". You
pass three parameters to the function: the path of the API request (everything
after https:/*coinbase.com/api/v1/), whether this API query is a GET or a POST,
and any parameters that go along with that GET or POST request. These params
first come into play here.

Let's make the API request:*/
$results = curling("https:/*coinbase.com/api/v1/" . $apiPath . "?" . http_build_query(array(
        "access_token" => $accessToken
    )), $getOrPost, $parameters);

/*Now we're going to make sure the request actually worked, and didn't get
rejected because the Access Token was expired. If it WAS expired, the
results should be blank. (It'll return a 401 if you want to get fancy.)*/
$resultsArray = json_decode($results);
if(count($resultsArray) < 1){

/*Looks like it did expire, so now we make a POST request using the Refresh
token, which will return a new Access Token AND a new Refresh Token.*/
    $reAuthorization = json_decode(curling(
        "https:/*coinbase.com/oauth/token?" . http_build_query(array(
            "grant_type" => "refresh_token",
            "code" => $userCode,
            "refresh_token" => $refreshToken
        )), "post", ""), true);
    $accessToken = $reAuthorization["access_token"];
    $refreshToken = $reAuthorization["refresh_token"];

/*Let's back those up to userdata.txt...*/
    $userData["accessToken"] = $accessToken;
    $userData["refreshToken"] = $refreshToken;
    file_put_contents("userdata.txt",json_encode($userData),LOCK_EX);

/*...and try the API request all over again:*/
    $results = curling("https:/*coinbase.com/api/v1/" . $apiPath . "?" . http_build_query(array(
            "access_token" => $accessToken
        )), $getOrPost, $parameters);

/*If it doesn't work THIS time, I'm going to clean out userdata.txt and ask
the user to try again. One of the codes probably got all mungled up.*/
    $resultsArray = json_decode($results);
    if(array_key_exists("error",$resultsArray)){
        file_put_contents("userdata.txt","",LOCK_EX);
        die("Something went wrong. Please refresh the page and try again.");
    }
}

/*If, however, everything went right, then this function will return the JSON
string with the data from the API! Hooray!*/
return $results;

}

/*Here are 4 different example requests you can make.*/

/*
echo oauthRequest("account/generate_receive_address","post","");

echo oauthRequest("buttons","post",'{
    "button": {
        "name": "test",
        "type": "buy_now",
        "price_string": ".01",
        "price_currency_iso": "USD"
    }
}');

echo oauthRequest("prices/buy","get",'{
    "qty": 1,
    "currency": "USD"
}');

echo oauthRequest("account/balance","get","");
*/

?>

Question 2

The fact that the API used to be so simple -- only needing a Key -- means it was pretty insecure. So they beefed up the security a week-ish ago. Here's the blog post:

http://blog.coinbase.com/post/75936737678/more-security-and-granular-control-with-the-new-api

Everyone now gets an API "Secret" in addition to an API Key. Whenever you make a request to the API, you have to include three parameters:

Your API Key.
A "nonce", which is a unique number that you use to identify something. In this case, every single request you make needs to have a new number, and each request's nonce has to be bigger than the one before it.
Your API "Signature". This is NOT your API "Secret".

The Signature is your nonce followed immediately by the full URL to which you're posting your request, parameters and all. This URL also contains the nonce, so the whole thing all together would look something like this:

12345https://coinbase.com/api/v1/buttons?nonce=12345&name=Socks&price=9.95

Then you take that whole thing and encode it as a "SHA256" hash. If you don't know what that means, don't panic -- you can do it in one line using a function PHP already has built in.

At any rate, I was having some trouble figuring all this out, so I spent a little while on it and put together this script, which makes GETing and POSTing to the API really easy. I'd love to hear people's thoughts!

<?php

function coinbaseRequest($what,$getOrPost,$parameters){

//Obviously, your API Key and Secret go here.
$apikey = "blahblahblah";
$apisecret = "blahblahblahblah";    
$nonce = file_get_contents("nonce.txt") + 1;
file_put_contents("nonce.txt", $nonce, LOCK_EX);

$url = "https://coinbase.com/api/v1/" . $what . "?nonce=" . $nonce;

if($parameters != ""){
$parameters = http_build_query(json_decode($parameters), true);
}

//Here I go, hashing the Signature! Thanks, PHP, for making this easy!

$signature = hash_hmac("sha256", $nonce . $url . $parameters, $apisecret);

$ch = curl_init();

curl_setopt_array($ch, array(
    CURLOPT_URL => $url,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => array(
        "ACCESS_KEY: " . $apikey,
        "ACCESS_NONCE: " . $nonce,
        "ACCESS_SIGNATURE: " . $signature
    )));

if($getOrPost == "post"){
curl_setopt_array($ch, array(
    CURLOPT_POSTFIELDS => $parameters,
    CURLOPT_POST => true,
));
}

$results = curl_exec($ch);
curl_close($ch);

echo $results;
}

//This is a POST example.
coinbaseRequest("buttons", "post", '{
    "button": {
    "name": "test",
    "price_string": "1.23",
    "price_currency_iso": "USD",
    "variable_price": true
    }
}');


//This is a GET example.
coinbaseRequest("account/balance", "get", false);

?>

Notes:

I tried using (microtime(true)*100) for my nonces. The problem is it makes a decimal number, and the last few digits kept getting dropped or rounded off so it didn't work. Then I thought, "Screw this", made a blank nonce.txt file, and wrote 1 in it, and to get nonces I just got the contents of that file, added 1, and replaced the file with the new number. It served a second purpose as a counter showing how many total requests I've made.

But then someone pointed out to me PHP's "uniqid" function, which generates an ID based on the current microtime. So you can also try this:
```
$nonce = hexdec(uniqid());
```
This has the advantage of not accessing an external file. I actually really like being able to see how many requests I've made, and so will probably stick with the (bad) nonce.txt method.
The coinbaseRequest() function has three parameters. The first is the directory to which you're making your request -- that is, whatever's supposed to come after "https://coinbase.com/api/v1/". The second parameter is "get" or "post", depending on whether it's a GET or a POST request. (Make sense?)

The third parameter is all the queries you're passing in your request. This should be formatted as JSON, unless it's a GET request that doesn't take any parameters (besides the Key, Nonce, and Signature which the function includes for you), in which case you should leave this as false.

EDIT, March 3rd:

I made a little function for taking whatever's returned by coinbaseRequest and turning it into a button:

function makebutt($data){

$data = json_decode($data,true);
$buttoncode = $data["button"]["code"];

return ("<a class=\"coinbase-button\" data-code=\"" . $buttoncode . "\" href=\"https://coinbase.com/checkouts/" . $buttoncode . "\">Pay With Bitcoin</a><script src=\"https://coinbase.com/assets/button.js\" type=\"text/javascript\"></script>");
}

Question 3

It's not working because Coinbase recently implemented the OAuth2 protocol. This ensures the personal information of your user is transmitted securely. I referred to this implementation several months ago when writing my own OAuth class on another project: