Verifies the assertion and the csrf token in the given request.

    Returns the email of the user if everything is valid, otherwise raises
    a HTTPBadRequest

def verify_login(request):
    """Verifies the assertion and the csrf token in the given request.

    Returns the email of the user if everything is valid, otherwise raises
    a HTTPBadRequest"""
    verifier = request.registry['persona.verifier']
    try:
        data = verifier.verify(request.POST['assertion'])
    except (ValueError, browserid.errors.TrustError) as e:
        logger.info('Failed persona login: %s (%s)', e, type(e).__name__)
        raise HTTPBadRequest('Invalid assertion')
    return data['email']