If you have an authorizing function shared across your app then it needs to be listed in each service.yml and the references to it from within that service.yml need to be namespaced in order for it to find the function. The following code works but is a bit yucky
functions:
authorize:
handler: src/authorize.handler
get:
handler: src/surveys.get
events:
- http:
path: /
method: get
cors: ${self:custom.cors}
authorizer: surveys-authorize
post:
handler: src/surveys.post
events:
- http:
path: /
method: post
cors: ${self:custom.cors}
authorizer: surveys-authorize