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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def signature_cert_chain_url(url):
 """Validate URL specified by SignatureCertChainUrl. See `validate.request` for additional info. Args: url: str. SignatureCertChainUrl header value sent by request. Returns: bool: True if valid, False otherwise. """

    r = urlparse(url)
    if not r.scheme.lower() == 'https':
        warnings.warn('Certificate URL scheme is invalid.')
        return False
    if not r.hostname.lower() == 's3.amazonaws.com':
        warnings.warn('Certificate URL hostname is invalid.')
        return False
    if not os.path.normpath(r.path).startswith('/echo.api/'):
        warnings.warn('Certificate URL path is invalid.')
        return False
    if r.port and not r.port == 443:
        warnings.warn('Certificate URL port is invalid.')
        return False
    return True