Caddyfile can use an Access Token instead of a JWT. Much smaller and correct for this OAuth2 configuration. This new value has been documented inline.

Likewise the `sub` field returned is not important to this test. `email_verified` is kept as it may be helpful for further coverage testing.

The actual test-case has better assertions for success and failure by checking for Dovecot logs we expect instead of netcat response.

`oauth2` to `auth` for the Caddy container hostname is not necessary, just a more generic subdomain choice.

This way is more flexible and doesn't require modifying the `Caddyfile` directly, while still easy to use.

Additionally simplifies understanding the Caddyfile to maintainers by removing the `route` directive that was required to ensure a deterministic order of vars.

Since this is the only intended usage, might as well have it respond with the full file content.

Caddyfile route for `/imap/` now accepts any subpath to support handling both `xoauth2` and `oauthbearer` subpaths.

Both SASL mechanisms represent the same information, with `XOAUTH2` being a common mechanism to encounter defined by Google, whilst `OAUTHBEARER` is the newer variant standardized by RFC 7628 but not yet as widely adopted.

The request to `/userinfo` endpoint will be the same, only the `credentials` value to be encoded differs.

Instead of repeating the block for a similar route, this difference is handled via the Caddyfile `map` directive.

We match the path context (_`/xoauth2` or `/oauthbearer`, the `/imap` prefix was stripped by `handle_path` earlier_), when there is a valid match, `sasl_mechanism` and `credentials` map vars are created and assigned to be referenced by the later `respond` directive.

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Repeat the same test-case logic, DRY with log asserts extracted to a common function call. This should be fine as the auth method will be sufficient to match against or a common failure caught.

Separate test cases and additional comment on creating the same base64 encoded credentials via CLI as an alternative to running Caddy.

Added a simple `compose.yaml` for troubleshooting or running the container for the `/imap/xoauth2` / `/imap/oauthbearer` endpoints.

`reverse_proxy` was a bit more convenient, but the additional internal ports weren't really relevant. It also added noise to logging when troubleshooting.

The `import` directive with Snippet blocks instead is a bit cleaner, but when used in a single file snippets must be defined prior to referencing them with the `import` directive.

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`compose.yaml` inlines the examples, with slight modification to `localhost:80`, since the Caddyfile examples `auth.example.test` is more relevant to the tests which can use it, and not applicable to troubleshooting locally outside of tests.