Support multiple required security schemes

[adlerfaulkner]

Currently this library only uses the first key of a security requirement object as the required security scheme. We should support all security schemes listed in a security requirement.

For example, an OpenAPI operation may have a security requirement of:

{
    "clientAuth": [],
    "userToken": []
}

Which corresponds to security schemes in such as:

{
    "components": {
        "securitySchemes": {
            "clientAuth": {
                "type": "http",
                "scheme": "bearer",
                "bearerFormat": "JWT",
                "description": "JWT to authenticate the client"
            },
            "userToken": {
                "type": "apiKey",
                "name": "X-Authorization-User",
                "in": "header",
                "description": "API key to authenticate users"
            }
        }
    }
}

Note: to support multiple schemes or type apiKey in one operation, the configuration argument should accept the api keys by their name rather than just apiKey. The apiKey field can be used as a backup if the name of the api key is not supplied. The same should NOT be true for security schemes of type http or oauth2 because they use a specific header format and support for multiple values are not defined in their specs.