oauth issue: access_token is never set

Description

I've had trouble getting Oauth working. The generated code wipes the token within the Authorization header and leaves just bearer as the value.

To expand further, within the generated configuration.py file, the auth_settings method is responsible for returning the respective auth method we use for a endpoint. You can see that for oauth, the value of value is set to "Bearer" + access_token. What happens though when access_token does not exist? It sets it to just Bearer. When I looked further into how access_token gets set, I found out that it doesn't even get set. It is set to "" by default and there is no code that ever attempts to update that. I also looked at the source code and it looks like "" is hard-coded for access_token.

def auth_settings(self):
        """
        Gets Auth Settings dict for api client.

        :return: The Auth Settings information dict.
        """
        return {
            'oauth':
                {
                    'type': 'oauth2',
                    'in': 'header',
                    'key': 'Authorization',
                    'value': 'Bearer' + access_token
                },
            'token':
                {
                    'type': 'api_key',
                    'in': 'header',
                    'key': 'Authorization',
                    'value': self.get_api_key_with_prefix('Authorization')
                },

        }

def __init__(self):
        ...
        # access token for OAuth
        self.access_token = ""
        ...

Swagger-codegen version

V2.2.3

Swagger declaration file content or url

https://raw.githubusercontent.com/datadotworld/dwapi-spec/master/src/main/resources/world/data/api/swagger.json

Command line used for generation

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

I fixed it by just checking if access_token exists before actually setting it.

Start with the generated configuration.py auth_settings method and the init access_token initialization shown in the report, then trace the source template that produces them. Reproduce the OAuth behavior using the linked Swagger declaration and verify that a configured access token is preserved in the Authorization header rather than producing only Bearer.