```
         /!\ this is a work in progress and will    /!\
         /!\ be force pushed until ready for review /!\
```

 ## 👀 overview

fixes #3627.

this reorganizes the logic in pd's startup code related to automatically
managed https functionality.

 ## 🎨 background & motivation

this PR, besides cleaning up the `rustls-acme`-related auto-https logic, is
also interested in *creating a state-of-affairs that will dovetail into
pr #3522*. in particular, this expression to start the GRPC serve given a
bound listener...

```rust
tokio::task::Builder::new()
    .name("grpc_server")
    .spawn(grpc_server.serve_with_incoming(tls_incoming))
    .expect("failed to spawn grpc server")
```

...should be adjusted so as to accept an `axum::Router`.

other tertiary requirements:
- when no `grpc_auto_https` flag has been configured, serve without using an ACME resolver
- ALPN permit http/1.1 for grpc-web backwards compatibility.

 ### ⚖️  `rustls-acme` and `tokio-rustls-acme`

quoth the #3627 description, citing an earlier comment:

> In the ~year since this code was written, there may be better options.
> `tokio-rustls-acme` seems promising
\- <#3522 (comment)>

for reference, the repositories for each live here, and here:
- <https://github.com/FlorianUekermann/rustls-acme>
- <https://github.com/n0-computer/tokio-rustls-acme>

after some comparison, i have come to the opinion that `rustls-acme` will still
be adequate for our purposes. the latter is a fork of the former, but active
development appears to have continued in the former, and i did not see any
particular "_must-have_" features for us in the latter.

 ## 🚰 dropping down to `axum`

(this part is lengthy...)

as stated above, we want to switch to an `axum::Router`. this means that
we won't be able to use the `AcmeConfig::incoming` function. the
`rustls-acme` library provides some "low-level" examples we can check
out:

- <https://github.com/FlorianUekermann/rustls-acme/blob/main/examples/low_level_tokio.rs>
- <https://github.com/FlorianUekermann/rustls-acme/blob/main/examples/low_level_axum.rs>

`low_level_axum` sounds promising, given that #3522 itself drops down
from tonic into axum. a catch is that the "axum" example is referring to
`axum-server`, a library that wraps `axum`, rather than `axum` itself.
more on that momentarily.

we also use `tonic` 0.10.2 in pd, and elsewhere in the penumbra
monorepo. tonic isn't using hyper 1.x yet. this was being worked on in
hyperium/tonic#1583, continued on in hyperium/tonic#1595, and tracked in
hyperium/tonic#1579. that work also depends upon hyperium/hyper#3461.

this is complicated by the fact that `axum-server` 0.6.0 depends on
`hyper` 1.1.0. this is particularly relevant because of
hyperium/hyper#3040. so, we must be mindful that there is now a
`tower::Service` and a `hyper::Service`. `hyper-util` provides
facilities to convert between the two, and other helper glue.
additionally, see the "_upgrading"_ migration guide for more information
on the differences between pre- and post-1.0 interfaces in `hyper`.

- https://hyper.rs/guides/1/upgrading/
- <https://docs.rs/hyper-util/latest/hyper_util/service/struct.TowerToHyperService.html>

at a high level we need to take our `tonic::Router`, and turn that into
a `MakeService`, some object that can be used to _generate_ `Service`
instances to process a request.

this is additionally complicated by the fact that `axum-server` defines
its _own_ `MakeService` trait. that trait is sealed, blanket
implemented, and is a bound included in
`axum_server::server::Server::serve`.

```rust
// axum_server::serve
impl Server {
    pub async fn serve<M>(self, mut make_service: M) -> io::Result<()>
    where
        M: MakeService<SocketAddr, Request<Incoming>>,
        // ...
    { todo!() }
}
```

the `SocketAddr` parameter above is of importance.

`axum::Router::into_make_service` gives us `IntoMakeService<Router>`
- <https://docs.rs/axum/latest/axum/routing/struct.IntoMakeService.html>

```rust
impl<S, T> Service<T> for IntoMakeService<S>
where
    S: Clone,
{
    type Response = S;
    type Error = Infallible;
    type Future = IntoMakeServiceFuture<S>;
```

...which means that we are faced with this error:

```
error[E0277]: the trait bound `Router: tower_service::Service<http::request::Request<hyper::body::incoming::Incoming>>` is not satisfied
   --> crates/bin/pd/src/auto_https.rs:62:20
    |
62  |             .serve(make_svc)
    |              ----- ^^^^^^^^ the trait `tower_service::Service<http::request::Request<hyper::body::incoming::Incoming>>` is not implemented for `Router`
    |              |
    |              required by a bound introduced by this call
    |
    = help: the trait `tower_service::Service<axum::http::Request<axum::body::Body>>` is implemented for `Router`
    = help: for that trait implementation, expected `axum::http::Request<axum::body::Body>`, found `http::request::Request<hyper::body::incoming::Incoming>`
    = note: required for `IntoMakeService<Router>` to implement `axum_server::service::MakeService<std::net::SocketAddr, http::request::Request<hyper::body::incoming::Incoming>>`
```

`axum::Router::into_make_service` does not play well with
`axum_server::Server`.

...and if we specify the new `hyper::body::incoming::Incoming` as the
body type for the axum router,

```
error[E0599]: the method `into_make_service` exists for struct `Router<(), Incoming>`, but its trait bounds were not satisfied
  --> crates/bin/pd/src/auto_https.rs:57:31
   |
57 |         let make_svc = router.into_make_service();
   |                               ^^^^^^^^^^^^^^^^^ method cannot be called on `Router<(), Incoming>` due to unsatisfied trait bounds
   |
  ::: /home/katie/.cargo/registry/src/index.crates.io-6f17d22bba15001f/hyper-1.1.0/src/body/incoming.rs:47:1
   |
47 | pub struct Incoming {
   | ------------------- doesn't satisfy `hyper::body::Incoming: HttpBody`
   |
   = note: the following trait bounds were not satisfied:
           `hyper::body::Incoming: HttpBody`
```

`HttpBody` was the pre-1.0 trait, that is now `Body` post-1.0. in short, there
are some incongruencies at play as different libraries catch up to the new
breaking changes in `hyper`.

 ## 🤨 ...so now what?

TODO(kate): write up course of action for tomorrow.

---

🟥 NB: i worry about breakage due to untested load-bearing behavior
during a migration like this. see "tertiary requirements", above.
consider this a PR to be suspect of when deploying a new testnet.

Refs: #3627
Refs: #3646
Refs: #3522

 ## 👀 overview

fixes #3627.

this reorganizes the logic in pd's startup code related to automatically
managed https functionality.

 ## 🎨 background & motivation

this PR, besides cleaning up the `rustls-acme`-related auto-https logic, is
also interested in *creating a state-of-affairs that will dovetail into
pr #3522*. in particular, this expression to start the GRPC serve given a
bound listener...

```rust
tokio::task::Builder::new()
    .name("grpc_server")
    .spawn(grpc_server.serve_with_incoming(tls_incoming))
    .expect("failed to spawn grpc server")
```

...should be adjusted so as to work with an `axum::Router`.

 ### ⚖️  `rustls-acme` and `tokio-rustls-acme`

quoth the #3627 description, citing an earlier comment:

> In the ~year since this code was written, there may be better options.
> `tokio-rustls-acme` seems promising
\- <#3522 (comment)>

for reference, the repositories for each live here, and here:
- <https://github.com/FlorianUekermann/rustls-acme>
- <https://github.com/n0-computer/tokio-rustls-acme>

after some comparison, i have come to the opinion that `rustls-acme` will still
be adequate for our purposes. the latter is a fork of the former, but active
development appears to have continued in the former, and i did not see any
particular "_must-have_" features for us in the latter.

 ## 🎴 changes

this commit moves some of the auto-https related code from the `main`
entrypoint, into standalone functions in `pd::main`.

some constants are defined, to keep control flow clear and to help
facilitate the addition of future options e.g. a flag to control the
LetsEncrypt environment to use.

 ## 🚰 dropping down to `axum`; a brief note on future upgrades

as stated above, we want to switch to an `axum::Router`. this means that
we won't be able to use the `AcmeConfig::incoming` function. the
`rustls-acme` library provides some "low-level" examples this work is
based upon

- <https://github.com/FlorianUekermann/rustls-acme/blob/main/examples/low_level_tokio.rs>
- <https://github.com/FlorianUekermann/rustls-acme/blob/main/examples/low_level_axum.rs>

we also use `tonic` 0.10.2 in pd, and elsewhere in the penumbra
monorepo. tonic isn't using hyper 1.x yet. this was being worked on in
hyperium/tonic#1583, continued on in hyperium/tonic#1595, and tracked in
hyperium/tonic#1579. that work also depends upon hyperium/hyper#3461.

we will need to be wait for tonic to finish its migration over to hyper
1.0, see:
hyperium/tonic#1579 (comment)

this is understandable, but i make note of this situation as a
signpost for our future selves when considering a migration to
recent versions of axum-server, axum, rustls-acme, or hyper.

for now, it's easiest to stay in lock-step with tonic, and we can revisit
the upgrade path(s) at a future date.

===

Refs: #3627
Refs: #3646
Refs: #3522

 ## 👀 overview

fixes #3627.

this reorganizes the logic in pd's startup code related to automatically
managed https functionality.

 ## 🎨 background & motivation

this PR, besides cleaning up the `rustls-acme`-related auto-https logic, is
also interested in *creating a state-of-affairs that will dovetail into
pr #3522*. in particular, this expression to start the GRPC serve given a
bound listener...

```rust
tokio::task::Builder::new()
    .name("grpc_server")
    .spawn(grpc_server.serve_with_incoming(tls_incoming))
    .expect("failed to spawn grpc server")
```

...should be adjusted so as to work with an `axum::Router`.

 ### ⚖️  `rustls-acme` and `tokio-rustls-acme`

quoth the #3627 description, citing an earlier comment:

> In the ~year since this code was written, there may be better options.
> `tokio-rustls-acme` seems promising
\- <#3522 (comment)>

for reference, the repositories for each live here, and here:
- <https://github.com/FlorianUekermann/rustls-acme>
- <https://github.com/n0-computer/tokio-rustls-acme>

after some comparison, i have come to the opinion that `rustls-acme` will still
be adequate for our purposes. the latter is a fork of the former, but active
development appears to have continued in the former, and i did not see any
particular "_must-have_" features for us in the latter.

 ## 🎴 changes

this commit moves some of the auto-https related code from the `main`
entrypoint, into standalone functions in `pd::main`.

some constants are defined, to keep control flow clear and to help
facilitate the addition of future options e.g. a flag to control the
LetsEncrypt environment to use.

 ## 🚰 dropping down to `axum`; a brief note on future upgrades

as stated above, we want to switch to an `axum::Router`. this means that
we won't be able to use the `AcmeConfig::incoming` function. the
`rustls-acme` library provides some "low-level" examples this work is
based upon

- <https://github.com/FlorianUekermann/rustls-acme/blob/main/examples/low_level_tokio.rs>
- <https://github.com/FlorianUekermann/rustls-acme/blob/main/examples/low_level_axum.rs>

we also use `tonic` 0.10.2 in pd, and elsewhere in the penumbra
monorepo. tonic isn't using hyper 1.x yet. this was being worked on in
hyperium/tonic#1583, continued on in hyperium/tonic#1595, and tracked in
hyperium/tonic#1579. that work also depends upon hyperium/hyper#3461.

we will need to be wait for tonic to finish its migration over to hyper
1.0, see:
hyperium/tonic#1579 (comment)

this is understandable, but i make note of this situation as a
signpost for our future selves when considering a migration to
recent versions of axum-server, axum, rustls-acme, or hyper.

for now, it's easiest to stay in lock-step with tonic, and we can revisit
the upgrade path(s) at a future date.

===

Refs: #3627
Refs: #3646
Refs: #3522