OAuthServer.php

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<?php

namespace ceLTIc\LTI\OAuth;

class OAuthServer
{

    protected $timestamp_threshold = 300; // in seconds, five minutes
    protected $version = '1.0';             // hi blaine
    protected $signature_methods = array();
    protected $data_store;

    function __construct($data_store)
    {
        $this->data_store = $data_store;
    }

    public function add_signature_method($signature_method)
    {
        $this->signature_methods[$signature_method->get_name()] = $signature_method;
    }

    // high level functions

    public function fetch_request_token(&$request)
    {
        $this->get_version($request);

        $consumer = $this->get_consumer($request);

        // no token required for the initial token request
        $token = NULL;

        $this->check_signature($request, $consumer, $token);

        // Rev A change
        $callback = $request->get_parameter('oauth_callback');
        $new_token = $this->data_store->new_request_token($consumer, $callback);

        return $new_token;
    }

    public function fetch_access_token(&$request)
    {
        $this->get_version($request);

        $consumer = $this->get_consumer($request);

        // requires authorized request token
        $token = $this->get_token($request, $consumer, "request");

        $this->check_signature($request, $consumer, $token);

        // Rev A change
        $verifier = $request->get_parameter('oauth_verifier');
        $new_token = $this->data_store->new_access_token($token, $consumer, $verifier);

        return $new_token;
    }

    public function verify_request(&$request)
    {
        $this->get_version($request);
        $consumer = $this->get_consumer($request);
        $token = $this->get_token($request, $consumer, "access");
        $this->check_signature($request, $consumer, $token);

        return array($consumer, $token);
    }

    // Internals from here

    private function get_version(&$request)
    {
        $version = $request->get_parameter("oauth_version");
        if (!$version) {
            // Service Providers MUST assume the protocol version to be 1.0 if this parameter is not present.
            // Chapter 7.0 ("Accessing Protected Ressources")
            $version = '1.0';
        }
        if ($version !== $this->version) {
            throw new OAuthException("OAuth version '$version' not supported");
        }

        return $version;
    }

    private function get_signature_method($request)
    {
        $signature_method = $request instanceof OAuthRequest ? $request->get_parameter('oauth_signature_method') : NULL;

        if (!$signature_method) {
            // According to chapter 7 ("Accessing Protected Ressources") the signature-method
            // parameter is required, and we can't just fallback to PLAINTEXT
            throw new OAuthException('No signature method parameter. This parameter is required');
        }

        if (!in_array($signature_method, array_keys($this->signature_methods))) {
            throw new OAuthException(
                "Signature method '$signature_method' not supported " .
                'try one of the following: ' .
                implode(', ', array_keys($this->signature_methods))
            );
        }

        return $this->signature_methods[$signature_method];
    }

    private function get_consumer($request)
    {
        $consumer_key = $request instanceof OAuthRequest ? $request->get_parameter('oauth_consumer_key') : NULL;

        if (is_null($consumer_key) || (strlen($consumer_key) <= 0)) {
            throw new OAuthException('Invalid consumer key');
        }

        $consumer = $this->data_store->lookup_consumer($consumer_key);
        if (!$consumer) {
            throw new OAuthException('Invalid consumer');
        }

        return $consumer;
    }

    private function get_token($request, $consumer, $token_type = "access")
    {
        $token_field = $request instanceof OAuthRequest ? $request->get_parameter('oauth_token') : NULL;

        $token = $this->data_store->lookup_token($consumer, $token_type, $token_field);
        if (!$token) {
            throw new OAuthException("Invalid $token_type token: $token_field");
        }

        return $token;
    }

    private function check_signature($request, $consumer, $token)
    {
        // this should probably be in a different method
        $timestamp = $request instanceof OAuthRequest ? $request->get_parameter('oauth_timestamp') : NULL;
        $nonce = $request instanceof OAuthRequest ? $request->get_parameter('oauth_nonce') : NULL;

        $this->check_timestamp($timestamp);
        $this->check_nonce($consumer, $token, $nonce, $timestamp);

        $signature_method = $this->get_signature_method($request);

        $signature = $request->get_parameter('oauth_signature');
        $valid_sig = $signature_method->check_signature($request, $consumer, $token, $signature);

        if (!$valid_sig) {
            throw new OAuthException('Invalid signature');
        }
    }

    private function check_timestamp($timestamp)
    {
        if (!$timestamp)
            throw new OAuthException('Missing timestamp parameter. The parameter is required');

        // verify that timestamp is recentish
        $now = time();
        if (abs($now - $timestamp) > $this->timestamp_threshold) {
            throw new OAuthException("Expired timestamp, yours $timestamp, ours $now");
        }
    }

    private function check_nonce($consumer, $token, $nonce, $timestamp)
    {
        if (!$nonce)
            throw new OAuthException('Missing nonce parameter. The parameter is required');

        // verify that the nonce is uniqueish
        $found = $this->data_store->lookup_nonce($consumer, $token, $nonce, $timestamp);
        if ($found) {
            throw new OAuthException("Nonce already used: $nonce");
        }
    }

}