servant-client with BasicAuth

Hi.

So I have an API as following:

```haskell
type MyAPI = BasicAuth "standard" ApiUser :> (EndpointA :<|> EndpointB :<|> EndpointC)
```

In order to produce a client from this, it seems I have to go through the extra pain of writing:

```haskell
clientA user = case cf user of
clientA' :<|> _ :<|> _ -> clientA'

clientB user = case cf user of
_ :<|> clientB' :<|> _ -> clientB'

clientC user = case cf user of
_ :<|> _ :<|> clientC' -> clientC'

cf = client (Proxy @MyAPI)
```

Having to pattern match repeatedly is very cumbersome (and requires modifying *every* endpoint if a single endpoint gets added).
Am I doing this wrong? Is there a combinator I'm not seeing?