Cloudfront and Lambda@Edge: Changing from a custom origin to an Amazon S3 origin

The AWS documentation shows the example: "Example: Use an origin request trigger to change from a custom origin to an Amazon S3 origin", where 'authMethod': 'origin-access-identity' is used.

I cannot get this to work. I receive the following error: "The Lambda function returned an invalid origin configuration, authentication configuration for S3 is invalid, authMethod should be of string type."

However, in the documentation for "Lambda@Edge event structure", AWS explicitly states: "You can't use an OAI when you change the request from a custom origin to an Amazon S3 origin."

https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-event-structure.html#example-origin-request

Hey @AWS, Does this example actually work? If not, it should be removed immediately to prevent wasting countless developer hours trying to make it work.

from urllib.parse import parse_qs

def lambda_handler(event, context):
    request = event['Records'][0]['cf']['request']
    '''
    Reads query string to check if S3 origin should be used, and
    if true, sets S3 origin properties
    '''
    params = {k: v[0] for k, v in parse_qs(request['querystring']).items()}
    if params.get('useS3Origin') == 'true':
        s3DomainName = 'amzn-s3-demo-bucket.s3.amazonaws.com'

        # Set S3 origin fields
        request['origin'] = {
            's3': {
                'domainName': s3DomainName,
                'region': '',
                'authMethod': 'origin-access-identity',
                'path': '',
                'customHeaders': {}
            }
        }
        request['headers']['host'] = [{'key': 'host', 'value': s3DomainName}]
    return request