Ensure AWS Lambda function permissions have a source ARN specified

AWS Lambda Permissions give an AWS service or account permission to use a function. Not configuring the source ARN for the lambda function permissions could allow unintended access. It is considered best practice to specify the source ARN in cloud services.

In AWS Console -

1. Sign in to AWS Console and go to the Functions page on the Lambda console.
2. Choose a function to update.
3. Select Configuration and then select Permissions.
4. Scroll down to Resource-based policy and then select View policy document and Set the Source ARN.
5. Select Save.

In Terraform -

1. In the aws_lambda_permission resource, set source_arn field accordingly.

References:
https://docs.aws.amazon.com/lambda/latest/dg/security-iam.html
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-permission.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/lambda_permission