`AuthResponse.context` type hints

It seems the `context` dictionary in `AuthResponse` has a type of `Dict[str, str]`. Is this intentional? I am getting type checking errors from mypy when I try to use integer as values:

https://github.com/aws/chalice/blob/185802a35530e8c2530aa6421cadbcdc505ce571/chalice/app.pyi#L292-L296

```
Dict entry 0 has incompatible type "str": "int"; expected "str": "str"mypy(error)
```

Start at chalice/app.pyi lines 292-296, where AuthResponse.context is annotated, and compare that annotation with the integer-valued usage described in the issue. Confirm the intended value type, then verify that mypy accepts valid context dictionaries without producing the reported error.

Written by the indexing model from the issue text.