Add header

---

• The function needs to return a dictionary with the status code and the headers.
• At least the Content-type.

examples/aws/hello_world_header.py

def lambda_handler(event, context):
    return {
        'statusCode': 200,
        'headers': { 'Content-Type': 'text/html' },
        'body': 'Hello World!'
    }

• curl ...