v1.20.0: Thancred Waters

The big ticket items are as follows:

- Implement a no-JS challenge method: [`metarefresh`](./admin/configuration/challenges/metarefresh.mdx) ([#95](https://github.com/TecharoHQ/anubis/issues/95))
- Implement request "weight", allowing administrators to customize the behaviour of Anubis based on specific criteria
- Implement GeoIP and ASN based checks via [Thoth](https://anubis.techaro.lol/docs/admin/thoth) ([#206](https://github.com/TecharoHQ/anubis/issues/206))
- Add [custom weight thresholds](./admin/configuration/thresholds.mdx) via CEL ([#688](https://github.com/TecharoHQ/anubis/pull/688))
- Move Open Graph configuration [to the policy file](./admin/configuration/open-graph.mdx)
- Enable support for Open Graph metadata to be returned by default instead of doing lookups against the target
- Add `robots2policy` CLI utility to convert robots.txt files to Anubis challenge policies using CEL expressions ([#409](https://github.com/TecharoHQ/anubis/issues/409))
- Refactor challenge presentation logic to use a challenge registry
- Allow challenge implementations to register HTTP routes
- [Imprint/Impressum support](./admin/configuration/impressum.mdx) ([#362](https://github.com/TecharoHQ/anubis/issues/362))
- Fix "invalid response" after "Success!" in Chromium ([#564](https://github.com/TecharoHQ/anubis/issues/564))

A lot of performance improvements have been made:

- Replace internal SHA256 hashing with xxhash for 4-6x performance improvement in policy evaluation and cache operations
- Optimized the OGTags subsystem with reduced allocations and runtime per request by up to 66%
- Replace cidranger with bart for IP range checking, improving IP matching performance by 3-20x with zero heap
  allocations

And some cleanups/refactors were added:

- Fix OpenGraph passthrough ([#717](https://github.com/TecharoHQ/anubis/issues/717))
- Remove the unused `/test-error` endpoint and update the testing endpoint `/make-challenge` to only be enabled in
  development
- Add `--xff-strip-private` flag/envvar to toggle skipping X-Forwarded-For private addresses or not
- Bump AI-robots.txt to version 1.37
- Make progress bar styling more compatible (UXP, etc)
- Add `--strip-base-prefix` flag/envvar to strip the base prefix from request paths when forwarding to target servers
- Fix an off-by-one in the default threshold config
- Add functionality for HS512 JWT algorithm
- Add support for dynamic cookie domains with the `--cookie-dynamic-domain`/`COOKIE_DYNAMIC_DOMAIN` flag/envvar

Request weight is one of the biggest ticket features in Anubis. This enables Anubis to be much closer to a Web Application Firewall and when combined with custom thresholds allows administrators to have Anubis take advanced reactions. For more information about request weight, see [the request weight section](./admin/policies.mdx#request-weight) of the policy file documentation.

TL;DR when you have one or more WEIGHT rules like this:

```yaml
bots:
  - name: gitea-session-token
    action: WEIGH
    expression:
      all:
        - '"Cookie" in headers'
        - headers["Cookie"].contains("i_love_gitea=")
    # Remove 5 weight points
    weight:
      adjust: -5
```

You can configure custom thresholds like this:

```yaml
thresholds:
  - name: minimal-suspicion # This client is likely fine, its soul is lighter than a feather
    expression: weight < 0 # a feather weighs zero units
    action: ALLOW # Allow the traffic through

  # For clients that had some weight reduced through custom rules, give them a
  # lightweight challenge.
  - name: mild-suspicion
    expression:
      all:
        - weight >= 0
        - weight < 10
    action: CHALLENGE
    challenge:
      # https://anubis.techaro.lol/docs/admin/configuration/challenges/metarefresh
      algorithm: metarefresh
      difficulty: 1
      report_as: 1

  # For clients that are browser-like but have either gained points from custom
  # rules or report as a standard browser.
  - name: moderate-suspicion
    expression:
      all:
        - weight >= 10
        - weight < 20
    action: CHALLENGE
    challenge:
      # https://anubis.techaro.lol/docs/admin/configuration/challenges/proof-of-work
      algorithm: fast
      difficulty: 2 # two leading zeros, very fast for most clients
      report_as: 2

  # For clients that are browser like and have gained many points from custom
  # rules
  - name: extreme-suspicion
    expression: weight >= 20
    action: CHALLENGE
    challenge:
      # https://anubis.techaro.lol/docs/admin/configuration/challenges/proof-of-work
      algorithm: fast
      difficulty: 4
      report_as: 4
```

These thresholds apply when no other `ALLOW`, `DENY`, or `CHALLENGE` rule matches the request. `WEIGHT` rules add and remove request weight as needed:

```yaml
bots:
  - name: gitea-session-token
    action: WEIGH
    expression:
      all:
        - '"Cookie" in headers'
        - headers["Cookie"].contains("i_love_gitea=")
    # Remove 5 weight points
    weight:
      adjust: -5

  - name: bot-like-user-agent
    action: WEIGH
    expression: '"Bot" in userAgent'
    # Add 5 weight points
    weight:
      adjust: 5
```

Of note: the default "generic browser" rule assigns 10 weight points:

```yaml
  # Generic catchall rule
- name: generic-browser
  user_agent_regex: >-
    Mozilla|Opera
  action: WEIGH
  weight:
    adjust: 10
```

Adjust this as you see fit.