Creating APIs without authentication unnecessarily increases the attack surface on the target infrastructure.

Unless another authentication method is used, attackers have the opportunity to attempt attacks against the underlying API.
This means attacks both on the functionality provided by the API and its infrastructure.

Ask Yourself Whether

• The underlying API exposes all of its contents to any anonymous Internet user.

There is a risk if you answered yes to this question.

Recommended Secure Coding Practices

In general, prefer limiting API access to a specific set of people or entities.

AWS provides multiple methods to do so:

• AWS_IAM, to use standard AWS IAM roles and policies.
• COGNITO_USER_POOLS, to use customizable OpenID Connect (OIDC) identity providers (IdP).
• CUSTOM, to use an AWS-independant OIDC provider, glued to the infrastructure with a Lambda authorizer.

Sensitive Code Example

For aws-cdk-lib.aws_apigateway.Resource:

import {aws_apigateway as apigateway} from "aws-cdk-lib"

const resource = api.root.addResource("example")
resource.addMethod(
    "GET",
    new apigateway.HttpIntegration("https://example.org"),
    {
        authorizationType: apigateway.AuthorizationType.NONE // Sensitive
    }
)

For aws-cdk-lib.aws_apigatewayv2.CfnRoute:

import {aws_apigatewayv2 as apigateway} from "aws-cdk-lib"

new apigateway.CfnRoute(this, "no-auth", {
    apiId: api.ref,
    routeKey: "GET /no-auth",
    authorizationType: "NONE", // Sensitive
    target: exampleIntegration
})

Compliant Solution

For aws-cdk-lib.aws_apigateway.Resource:

import {aws_apigateway as apigateway} from "aws-cdk-lib"

const resource = api.root.addResource("example",{
    defaultMethodOptions:{
        authorizationType: apigateway.AuthorizationType.IAM
    }
})
resource.addMethod(
    "POST",
    new apigateway.HttpIntegration("https://example.org"),
    {
        authorizationType: apigateway.AuthorizationType.IAM
    }
)
resource.addMethod(  // authorizationType is inherited from the Resource's configured defaultMethodOptions
    "GET"
)

For aws-cdk-lib.aws_apigatewayv2.CfnRoute:

import {aws_apigatewayv2 as apigateway} from "aws-cdk-lib"

new apigateway.CfnRoute(this, "auth", {
    apiId: api.ref,
    routeKey: "POST /auth",
    authorizationType: "AWS_IAM",
    target: exampleIntegration
})

See

• AWS Documentation - Controlling and managing access to a REST API in API Gateway
• OWASP Top 10 2021 Category A1 - Broken Access Control
• MITRE, CWE-284 - Improper Access Control
• OWASP Top 10 2017 Category A5 - Broken Access Control