Add Cognito Post Confirmation example (#884)

- Show how to work with Cognito's Post Confirmation events.
- Make response generic so customers can return a different object as reponse.

Signed-off-by: David Calavera <david.calavera@gmail.com>

examples/basic-cognito-post-confirmation/.gitignore

@@ -0,0 +1 @@
+/target

examples/basic-cognito-post-confirmation/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "basic-cognito-post-confirmation"
+version = "0.1.0"
+edition = "2021"
+
+# Starting in Rust 1.62 you can use `cargo add` to add dependencies 
+# to your project.
+#
+# If you're using an older Rust version,
+# download cargo-edit(https://github.com/killercup/cargo-edit#installation) 
+# to install the `add` subcommand.
+#
+# Running `cargo add DEPENDENCY_NAME` will
+# add the latest version of a dependency to the list,
+# and it will keep the alphabetic ordering for you.
+
+[dependencies]
+aws-config = "1.5.0"
+aws-sdk-ses = "1.28.0"
+aws_lambda_events = { path = "../../lambda-events", default-features = false, features = ["cognito"] }
+
+lambda_runtime = { path = "../../lambda-runtime" }
+tokio = { version = "1", features = ["macros"] }
+

examples/basic-cognito-post-confirmation/README.md

@@ -0,0 +1,15 @@
+# Cognito Post Confirmation Request example
+
+This example shows how to write a Lambda function in Rust to process Cognito's Post Confirmation requests.
+
+This is a translation of the example in the AWS Docs to Rust: https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-post-confirmation.html#aws-lambda-triggers-post-confirmation-example
+
+## Build & Deploy
+
+1. Install [cargo-lambda](https://github.com/cargo-lambda/cargo-lambda#installation)
+2. Build the function with `cargo lambda build --release`
+3. Deploy the function to AWS Lambda with `cargo lambda deploy`
+
+## Build for ARM 64
+
+Build the function with `cargo lambda build --release --arm64`

examples/basic-cognito-post-confirmation/src/main.rs

@@ -0,0 +1,60 @@
+use aws_config::BehaviorVersion;
+use aws_lambda_events::event::cognito::CognitoEventUserPoolsPostConfirmation;
+use aws_sdk_ses::{
+    types::{Body, Content, Destination, Message},
+    Client,
+};
+use lambda_runtime::{run, service_fn, tracing, Error, LambdaEvent};
+
+const SOURCE_EMAIL: &str = "<source_email>";
+
+async fn function_handler(
+    client: &aws_sdk_ses::Client,
+    event: LambdaEvent<CognitoEventUserPoolsPostConfirmation>,
+) -> Result<CognitoEventUserPoolsPostConfirmation, Error> {
+    let payload = event.payload;
+
+    if let Some(email) = payload.request.user_attributes.get("email") {
+        let body = if let Some(name) = payload.request.user_attributes.get("name") {
+            format!("Welcome {name}, you have been confirmed.")
+        } else {
+            "Welcome, you have been confirmed.".to_string()
+        };
+        send_post_confirmation_email(client, email, "Cognito Identity Provider registration completed", &body).await?;
+    }
+
+    // Cognito always expect a response with the same shape as
+    // the event when it handles Post Confirmation triggers.
+    Ok(payload)
+}
+
+async fn send_post_confirmation_email(client: &Client, email: &str, subject: &str, body: &str) -> Result<(), Error> {
+    let destination = Destination::builder().to_addresses(email).build();
+    let subject = Content::builder().data(subject).build()?;
+    let body = Content::builder().data(body).build()?;
+
+    let message = Message::builder()
+        .body(Body::builder().text(body).build())
+        .subject(subject)
+        .build();
+
+    client
+        .send_email()
+        .source(SOURCE_EMAIL)
+        .destination(destination)
+        .message(message)
+        .send()
+        .await?;
+
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Error> {
+    tracing::init_default_subscriber();
+
+    let config = aws_config::load_defaults(BehaviorVersion::latest()).await;
+    let client = Client::new(&config);
+
+    run(service_fn(|event| function_handler(&client, event))).await
+}

lambda-events/src/event/cognito/mod.rs

@@ -84,13 +84,18 @@ pub enum CognitoEventUserPoolsPreAuthenticationTriggerSource {
 /// allowing the Lambda to send custom messages or add custom logic.
 #[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq, Serialize)]
 #[serde(rename_all = "camelCase")]
-pub struct CognitoEventUserPoolsPostConfirmation {
+pub struct CognitoEventUserPoolsPostConfirmation<T = CognitoEventUserPoolsPostConfirmationResponse>
+where
+    T: DeserializeOwned,
+    T: Serialize,
+{
     #[serde(rename = "CognitoEventUserPoolsHeader")]
     #[serde(flatten)]
     pub cognito_event_user_pools_header:
         CognitoEventUserPoolsHeader<CognitoEventUserPoolsPostConfirmationTriggerSource>,
     pub request: CognitoEventUserPoolsPostConfirmationRequest,
-    pub response: CognitoEventUserPoolsPostConfirmationResponse,
+    #[serde(bound = "")]
+    pub response: T,
 }
 
 #[derive(Clone, Debug, Deserialize, Eq, PartialEq, Serialize, Default)]
@@ -254,6 +259,7 @@ pub struct CognitoEventUserPoolsPostConfirmationRequest {
 /// `CognitoEventUserPoolsPostConfirmationResponse` contains the response portion of a PostConfirmation event
 #[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq, Serialize)]
 pub struct CognitoEventUserPoolsPostConfirmationResponse {}
+
 /// `CognitoEventUserPoolsPreTokenGenRequest` contains request portion of PreTokenGen event
 #[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq, Serialize)]
 #[serde(rename_all = "camelCase")]