I’ve spent today implementing Cognito with AWS SAM and it took quite a while to work out what needed to be done – unfortunately there’s a lot of conflicting doco out there. Posting a sample template just in case it’s able to help anyone else out.
The first thing to do is to explicitly define you rest API. By default AWS SAM will generate one with a default logical id of ServerlessRestApi. You’ll need to override this:
# See links for more info
# Referencing cognito authorizer: https://github.com/awslabs/serverless-application-model/issues/512#issuecomment-411284092
# Logical id is auto generated: https://github.com/awslabs/serverless-application-model/blob/master/docs/internals/generated_resources.rst#api
# Sample template.yml: https://github.com/awslabs/serverless-application-model/blob/release/v1.8.0/examples/2016-10-31/api_cognito_auth/template.yaml
Auth: # We will eventually define other auth options here such as Usage Plans/Api Keys, AWS_IAM, and Resource Policies
UserPoolArn: !GetAtt MyCustomCognitoUserPool.Arn # Can be a string, or array
# Identity: # Optional
# Header: ... # Optional; Default: Authorization
# ValidationExpression: ... # Optional; ensures the request header matches a pattern before checking in with the Authorizer endpoint; is there a default we can set for Cognito User Pools Auth?
You’ll also need to create a user pool and client:
You then add the api id and the auth attribute to each of your function properties. If you’ve used the default authorizer property when defining the associated api you can override it by using authorizer: none.
I ran into the following error while using the AWS SAM Cli:
Error: Invalid value for "--parameter-overrides": ParameterKey=PURPLE_FROG,ParameterValue=CatBreeds is not in valid format. It must look something like 'ParameterKey=KeyPairName,ParameterValue=MyKey ParameterKey=InstanceType,ParameterValue=t1.micro'
This is the command I was running:
sam local start-api --parameter-overrides "ParameterKey=PURPLE_FROG,ParameterValue=CatBreeds"
The error message is unfortunately very misleading. After a fair bit of testing I found that the cause is actually the underscore in the parameter key and has nothing to do with the command format. Renaming all of the parameters to something like “PURPLEFROG” works.