docs & changelog

CHANGELOG.md

@@ -173,6 +173,7 @@ you might end up in a situation where you don't have an ability to get it.
 - Attachment dimensions and blurhashes are federated when available.
 - Mastodon API: support `poll` notification.
 - Pinned posts federation
+- Possibility to discover users like `user@example.org`, while Pleroma is working on `pleroma.example.org`. Additional configuration required.
 
 ### Fixed
 - Don't crash so hard when email settings are invalid.

docs/docs/configuration/how_to_serve_another_domain_for_webfinger.md

@@ -0,0 +1,60 @@
+# How to use a different domain name for Pleroma and the users it serves
+
+Pleroma users are primarily identified by a `user@example.org` handle, and you might want this identifier to be the same as your email or jabber account, for instance.
+However, in this case, you are almost certainly serving some web content on `https://example.org` already, and you might want to use another domain (say `pleroma.example.org`) for Pleroma itself.
+
+Pleroma supports that, but it might be tricky to set up, and any error might prevent you from federating with other instances.
+
+## Account identifiers
+
+It is important to understand that for federation purposes, a user in Pleroma has two unique identifiers associated:
+
+- A webfinger `acct:` URI, used for discovery and as a verifiable global name for the user across Pleroma instances. In our example, our account's acct: URI is `acct:user@example.org`
+- An author/actor URI, used in every other aspect of federation. This is the way in which users are identified in ActivityPub, the underlying protocol used for federation with other Pleroma instances.
+In our case, it is `https://pleroma.example.org/users/user`.
+
+Both account identifiers are unique and required for Pleroma. An important risk if you set up your Pleroma instance incorrectly is to create two users (with different acct: URIs) with conflicting author/actor URIs.
+
+## WebFinger
+
+As said earlier, each Pleroma user has an `acct`: URI, which is used for discovery and authentication. When you add @user@example.org, a webfinger query is performed. This is done in two steps:
+
+1. Querying `https://example.org/.well-known/host-meta` (where the domain of the URL matches the domain part of the `acct`: URI) to get information on how to perform the query.
+This file will indeed contain a URL template of the form `https://example.org/.well-known/webfinger?resource={uri}` that will be used in the second step.
+2. Fill the returned template with the `acct`: URI to be queried and perform the query: `https://example.org/.well-known/webfinger?resource=acct:user@example.org`
+
+## Configuring your Pleroma instance
+
+**_DO NOT ATTEMPT TO CONFIGURE YOUR INSTANCE THIS WAY IF YOU DID NOT UNDERSTAND THE ABOVE_**
+
+### Configuring Pleroma
+
+Pleroma has a two configuration settings to enable using different domains for your users and Pleroma itself. `host` in `Pleroma.Web.Endpoint` and `domain` in `Pleroma.Web.WebFinger`. When the latter is not set, it defaults to the value of `host`.
+
+*Be extra careful when configuring your Pleroma instance, as changing `host` may cause remote instances to register different accounts with the same author/actor URI, which will result in federation issues!*
+
+```elixir
+config :pleroma, Pleroma.Web.Endpoint,
+  url: [host: "pleroma.example.org"]
+
+config :pleroma, Pleroma.Web.WebFinger, domain: "example.org"
+```
+
+- `domain` - is the domain for which your Pleroma instance has authority, it's the domain used in `acct:` URI. In our example, `domain` would be set to `example.org.
+- `host` - is the domain used for any URL generated for your instance, including the author/actor URL's. In our case, that would be `pleroma.example.org.
+
+### Configuring WebFinger domain
+
+Now, you have Pleroma running at `https://pleroma.example.org` as well as a website at `https://example.org`. If you recall how webfinger queries work, the first step is to query `https://example.org/.well-known/host-meta`, which will contain an URL template.
+
+Therefore, the easiest way to configure `example.org` is to redirect `/.well-known/host-meta` to `pleroma.example.org`.
+
+With nginx, it would be as simple as adding:
+
+```nginx
+location = /.well-known/host-meta {
+       return 301 https://pleroma.example.org$request_uri;
+}
+```
+
+in example.org's server block.