This is a follow up guide for How to create authentic digital certificate for your online course.

In this guide, you will learn how to use Airtable to automate the process you learn from the previous guide.

If you're not familiar with Airtable, you should definitely check them out and it is a very capable tool that everyone especially marketers should have in their tool belt.

How to

Deploying AWS Lambda Function

In order to generate the signed URL, you need a convenient place to serve the script and to call it through a simple trigger. AWS Lambda function fits the bill.

Creating Lambda Function

Create a new lambda function named secure_signed_image.
Paste the following modified code. In this example, the modification is similar to what we had from the previous guide. It is modified to work with AWS lambda function.

PYTHON
    import json
    import hmac
    import hashlib
    import base64

    def base64_encode(string):
        """
        Removes any `=` used as padding from the encoded string.
        """
        encoded = base64.b64encode(string.encode())
        encoded = encoded.rstrip(b'=')
        return encoded

    def generate_url(candidate):
      user_id = ""
      secret_key = ""
      base_id = ""

      modifications = [
        { "name": "text_candidate", "text": candidate }
      ]

      # ensure no spaces in json output
      encoded = json.dumps(modifications, separators=(',', ':'))
      encoded = base64_encode(encoded).decode()

      parameters = "{user_id}+{base_id}+{modifications}".format(user_id=user_id, base_id=base_id, modifications=encoded)

      signature = hmac.new(secret_key.encode(), parameters.encode(), hashlib.sha256).hexdigest()

      url = "https://images.usestencil.com/signed-images/{user_id}/{base_id}.png?modifications={modifications}&s={signature}".format(
          base_id=base_id,
          user_id=user_id,
          modifications=encoded,
          signature=signature
      )

      return url


    def lambda_handler(event, context):
        # we read the name from the query string
        # i.e. https://xxx.amazonaws.com/default/secure_signed_image?name=David
        candidate = event["queryStringParameters"]["name"]

        url = generate_url(candidate)
        resp = {
            "url": url
        }

        return {
            'statusCode': 200,
            'body': json.dumps(resp)
        }

Creating HTTP trigger

We need to set up HTTP trigger so we can call the URL publicly and execute our lambda function. One additional step we need to take care of is to ensure our trigger is proxied to our lambda so we can capture the query string properly.

Video Guide

The following video shows the setup one-by-one.

Airtable as database

We will get our candidates' name from table in Airtable. Airtable needs to be set in certain ways to allow for Integromat integration. We will also use Integromat to help tie everything together.

Generated signed URL will be populated into Signed URL column

For this example, we create 3 columns in which 2 columns are text and the last column (Last Modified) is a special Airtable column that tracks the last modified time.

For this particular column, we only set the last modified time when the Name column is updated.

See the video for the process

Setting up automation

Using Integromat

Now that we have launched our function to AWS Lambda and Airtable is ready for integration, we can call the lambda function any time to get back the signed URL.

The workflow basically works like this,

Airtable module watches for record update (this is why we need the Last Modified column)
Get the value from the Name column and send a GET request to our lambda function with the name as a query string parameter. We also URL encode it.
Once we get back the URL, we update the related record with the generated signed URL.

You can work on similar integration with Google Sheet.

How To Use Airtable To Automate Authentic Digital Certificate Creation