AuthBucket\OAuth2\TokenType\BearerTokenTypeHandler::getAccessToken PHP Method

    public function getAccessToken(Request $request)
    {
        $tokenHeaders = $request->headers->get('Authorization', false);
        if ($tokenHeaders && preg_match('/Bearer\\s*([^\\s]+)/', $tokenHeaders, $matches)) {
            $tokenHeaders = $matches[1];
        } else {
            $tokenHeaders = false;
        }
        $tokenRequest = $request->request->get('access_token', false);
        $tokenQuery = $request->query->get('access_token', false);
        // At least one (and only one) of client credentials method required.
        if (!$tokenHeaders && !$tokenRequest && !$tokenQuery) {
            throw new InvalidRequestException(['error_description' => 'The request is missing a required parameter.']);
        } elseif ($tokenHeaders && $tokenRequest || $tokenRequest && $tokenQuery || $tokenQuery && $tokenHeaders) {
            throw new InvalidRequestException(['error_description' => 'The request includes multiple credentials.']);
        }
        // Check with HTTP basic auth if exists.
        $accessToken = $tokenHeaders ?: $tokenRequest ?: $tokenQuery;
        // access_token must be in valid format.
        $errors = $this->validator->validate($accessToken, [new NotBlank(), new AccessToken()]);
        if (count($errors) > 0) {
            throw new InvalidRequestException(['error_description' => 'The request includes an invalid parameter value.']);
        }
        return $accessToken;
    }