64 lines
2.8 KiB
ReStructuredText
64 lines
2.8 KiB
ReStructuredText
Domains
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=======
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One of our key design features in Takahē is that we support multiple different
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domains for ActivityPub users to be under.
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As a server administrator, you do this by specifying one or more Domains on
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your server that users can make Identities (posting accounts) under.
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Domains can take two forms:
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* **Takahē lives on and serves the domain**. In this case, you just set the domain
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to point to Takahē and ensure you have a matching domain record; ignore the
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"service domain" setting.
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* **Takahē handles accounts under the domain but does not live on it**. For
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example, you wanted to service the ``@andrew@aeracode.org`` handle, but there
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is already a site on ``aeracode.org``, and Takahē instead must live elsewhere
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(e.g. ``fedi.aeracode.org``).
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In this second case, you need to have a *service domain* - a place where
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Takahē and the Actor URIs for your users live, but which is different to your
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main domain you'd like the account handles to contain.
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To set this up, you need to:
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* Choose a service domain and point it at Takahē. *You cannot change this
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domain later without breaking everything*, so choose very wisely.
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* On your primary domain, forward the URLs ``/.well-known/webfinger``,
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``/.well-known/nodeinfo`` and ``/.well-known/host-meta`` to Takahē.
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* Set up a domain with these separate primary and service domains in its
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record.
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Technical Details
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-----------------
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At its core, ActivityPub is a system built around URIs; the
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``@username@domain.tld`` format is actually based on Webfinger, a different
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standard, and merely used to discover the Actor URI for someone.
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Making a system that allows any Webfinger handle to be accepted is relatively
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easy, but unfortunately this is only how users are discovered via mentions
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and search; when an incoming Follow comes in, or a Post is boosted onto your
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timeline, you have to discover the user's Webfinger handle
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*from their Actor URI* and this is where it gets tricky.
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Mastodon, and from what we can tell most other implementations, do this by
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taking the ``preferredUsername`` field from the Actor object, the domain from
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the Actor URI, and webfinger that combination of username and domain. This
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means that the domain you serve the Actor URI on must uniquely map to a
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Webfinger handle domain - they don't need to match, but they do need to be
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translatable into one another.
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Takahē handles all this internally, however, with a concept of Domains. Each
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domain has a primary (display) domain name, and an optional "service" domain;
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the primary domain is what we will use for the user's Webfinger handle, and
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the service domain is what their Actor URI is served on.
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We look at ``HOST`` headers on incoming requests to match users to their
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domains, though for Actor URIs we ensure the domain is in the URI anyway.
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