Unable to implement an extractor the references my app-specific server context

I was looking to implement an ExclusiveExtractor that references data in my server context, and at first glance I thought I was going to be able to, but now I'm not seeing how I can specify my concrete type to be able to do so.
I want to do something like:

#[async_trait]
impl<T> ExclusiveExtractor for VerifiedGithubBody<T>
where
    T: Sync + Send,
{
    async fn from_request(
        rqctx: &RequestContext<MyContext>,
        request: hyper::Request<hyper::Body>,
    ) -> Result<Self, HttpError> {
        let context = rqctx.context();
        let hmac_secret = context.github_hmac_secret;

        ...
    }
...
}

where MyContext is:

pub(crate) struct MyContext{
    pub(crate) github_hmac_secret: secrecy::SecretString,
}

but that doesn't work.

I can do all the work of this in the endpoint handler, which is fine, but it would be my preference to do this kind of thing in an extractor. Alternatively, I could pass that access that data via other means, such as environment variables, but it is also my preference to not use that for secrets. The server context seems like an appropriate place to store that.

Start with the ExclusiveExtractor and RequestContext definitions, then trace how MyContext is created and made available to request handling. Compare the desired VerifiedGithubBody usage with the current extractor contract; done means the supported approach for accessing app-specific context is clear, or the required API change is precisely scoped.