OAuthSignatureMethod_HMAC_SHA256.php

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<?php

namespace IMSGlobal\LTI\OAuth;

class OAuthSignatureMethod_HMAC_SHA256 extends OAuthSignatureMethod {

    function get_name() {
        return "HMAC-SHA256";
    }

    public function build_signature($request, $consumer, $token) {

        $base_string = $request->get_signature_base_string();
        $request->base_string = $base_string;

        $key_parts = array(
          $consumer->secret,
          ($token) ? $token->secret : ""
        );

        $key_parts = OAuthUtil::urlencode_rfc3986($key_parts);
        $key = implode('&', $key_parts);

        return base64_encode(hash_hmac('sha256', $base_string, $key, true));

    }

}