Cognito User Pool Lambda Trigger permission - amazon-web-services

Question

I'm using Terraform to create a Cognito User pool. I'd like to use a lambda function for sending a custom message when a user signs up. When I run attempt to sign up on the client, I get an error saying that "CustomMessage invocation failed due to error AccessDeniedException." I've used Lambda Permissions before, but I can't find any examples of this configuration. How do I give the lambda function permission? The following is my current configuration.
resource "aws_cognito_user_pool" "main" {
name = "${var.user_pool_name}_${var.stage}"
username_attributes = [ "email" ]
schema {
attribute_data_type = "String"
mutable = true
name = "name"
required = true
}
schema {
attribute_data_type = "String"
mutable = true
name = "email"
required = true
}
password_policy {
minimum_length = "8"
require_lowercase = true
require_numbers = true
require_symbols = true
require_uppercase = true
}
mfa_configuration = "OFF"
lambda_config {
custom_message = aws_lambda_function.custom_message.arn
post_confirmation = aws_lambda_function.post_confirmation.arn
}
}
...
resource "aws_lambda_permission" "get_blog" {
statement_id = "AllowExecutionFromCognito"
action = "lambda:InvokeFunction"
function_name = aws_lambda_function.custom_message.function_name
principal = "cognito-idp.amazonaws.com"
source_arn = "${aws_cognito_user_pool.main.arn}/*/*"
depends_on = [ aws_lambda_function.custom_message ]
}
...
resource "aws_lambda_function" "custom_message" {
filename = "${var.custom_message_path}/${var.custom_message_file_name}.zip"
function_name = var.custom_message_file_name
role = aws_iam_role.custom_message.arn
handler = "${var.custom_message_file_name}.handler"
source_code_hash = filebase64sha256("${var.custom_message_path}/${var.custom_message_file_name}.zip")
runtime = "nodejs12.x"
timeout = 10
layers = [ var.node_layer_arn ]
environment {
variables = {
TABLE_NAME = var.table_name
RESOURCENAME = "blogAuthCustomMessage"
REGION = "us-west-2"
}
}
tags = {
Name = var.developer
}
depends_on = [
data.archive_file.custom_message,
]
}

Answer 1

Based on OP's feedback in the comment section, changing source_arn property in the aws_lambda_permission.get_blog to aws_cognito_user_pool.main.arn works.