feat: add post confirmation lambda hook

signup-lambda/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "signup-lambda"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+
+lambda_runtime = "1.0.1"
+aws-sdk-cognitoidentityprovider = "1.105.0"
+serde = "1"
+tokio = { version = "1", features = ["macros"] }
+aws-config = "1.8.12"