Introduce some metrics about endpoints and their arguments/outcomes

Author: shepmaster

ui/Cargo.lock

@@ -29,6 +29,8 @@ router = "0.6.0"
 openssl-probe = "0.1.2"
 dotenv = "0.15.0"
 snafu = "0.6.0"
+prometheus = "0.12.0"
+strum = { version = "0.20.0", features = ["derive"] }
 
 [dependencies.playground-middleware]
 git = "https://github.com/integer32llc/playground-middleware"

ui/Cargo.toml

@@ -6,15 +6,16 @@ disk in this directory.
 In production, these should be set according to your deployment method
 of choice.
 
-| Key                       | Required | Default Value   | Description                                                             |
-| --------------------------|----------|-----------------|-------------------------------------------------------------------------|
-| `PLAYGROUND_UI_ROOT`      | **Yes**  |                 | The path to the HTML, CSS, and Javascript files                         |
-| `PLAYGROUND_GITHUB_TOKEN` | **Yes**  |                 | The [GitHub API token][gist] to read and write Gists                    |
-| `PLAYGROUND_UI_ADDRESS`   | No       |       127.0.0.1 | The address to listen on                                                |
-| `PLAYGROUND_UI_PORT`      | No       |            5000 | The port to listen on                                                   |
-| `PLAYGROUND_LOG_FILE`     | No       |  access-log.csv | The file to record accesses                                             |
-| `PLAYGROUND_CORS_ENABLED` | No       |                 | If set, will enable CORS support                                        |
-| `TMPDIR`                  | No       | system-provided | Where compilation artifacts will be saved. Must be accessible to Docker |
+| Key                        | Required   | Default Value     | Description                                                               |
+| -------------------------- | ---------- | ----------------- | ------------------------------------------------------------------------- |
+| `PLAYGROUND_UI_ROOT`       | **Yes**    |                   | The path to the HTML, CSS, and Javascript files                           |
+| `PLAYGROUND_GITHUB_TOKEN`  | **Yes**    |                   | The [GitHub API token][gist] to read and write Gists                      |
+| `PLAYGROUND_UI_ADDRESS`    | No         | 127.0.0.1         | The address to listen on                                                  |
+| `PLAYGROUND_UI_PORT`       | No         | 5000              | The port to listen on                                                     |
+| `PLAYGROUND_LOG_FILE`      | No         | access-log.csv    | The file to record accesses                                               |
+| `PLAYGROUND_METRICS_TOKEN` | No         |                   | If set, will require authentication for the metrics endpoint              |
+| `PLAYGROUND_CORS_ENABLED`  | No         |                   | If set, will enable CORS support                                          |
+| `TMPDIR`                   | No         | system-provided   | Where compilation artifacts will be saved. Must be accessible to Docker   |
 
 [dotenv]: https://crates.io/crates/dotenv
 [gist]: https://developer.github.com/v3/gists/#authentication