src/Soap/Client.php
public function setHeader($header, $value)
    {
        if (strlen($header) < 1) {
            throw new Exception('Header must be a string.');
        }
        $this->customHeaders[$header] = $value;
        return $this;
    }
public function setHeader($header, $value)
    {
        if (strlen($header) < 1) {
            throw new Exception('Header must be a string.');
        }
        $this->customHeaders[$header] = $value;
        return $this;
    }
Sets a custom header to be sent together with the request.
Throws an exception if header's name is not at least 1 char long.

@param string $header
@param string $value
@return $this
@throws Exception