fedimovies/FEDERATION.md

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# ActivityPub federation in Mitra
Mitra largely follows the [ActivityPub](https://www.w3.org/TR/activitypub/) server-to-server specification but it makes uses of some non-standard extensions, some of which are required for interacting with it.
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The following activities are supported:
- Accept(Follow)
- Reject(Follow)
- Undo(Follow)
- Create(Note)
- Delete(Note)
- Like(Note)
- Undo(Like)
- Announce(Note)
- Undo(Announce)
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- Update(Note)
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- Follow(Person)
- Update(Person)
- Move(Person)
- Delete(Person)
- Add(Person)
- Remove(Person)
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And these additional standards:
- [Http Signatures](https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures)
- [NodeInfo](https://nodeinfo.diaspora.software/)
- [WebFinger](https://webfinger.net/)
Activities are implemented in way that is compatible with Pleroma, Mastodon and other popular ActivityPub servers.
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Supported FEPs:
- [FEP-f1d5: NodeInfo in Fediverse Software](https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-f1d5.md)
- [FEP-e232: Object Links](https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-e232.md)
- [FEP-8b32: Object Integrity Proofs](https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-8b32.md)
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## Object integrity proofs
All outgoing activities are signed with actor's key in accordance with [FEP-8b32](https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-8b32.md) document.
Example:
```json
{
"@context": "https://www.w3.org/ns/activitystreams",
"actor": "https://example.com/users/alice",
"cc": [],
"id": "https://example.com/objects/0185f5f8-10b5-1b69-f45e-25f06792f411",
"object": "https://example.net/users/bob/posts/141892712081205472",
"proof": {
"created": "2023-01-28T01:22:40.183273595Z",
"proofPurpose": "assertionMethod",
"proofValue": "z5djAdMSrV...",
"type": "MitraJcsRsaSignature2022",
"verificationMethod": "https://example.com/users/alice#main-key"
},
"to": [
"https://example.net/users/bob",
"https://www.w3.org/ns/activitystreams#Public"
],
"type":"Like"
}
```
### Supported proof suites
#### MitraJcsRsaSignature2022
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Canonicalization algorithm: JCS
Hashing algorithm: SHA-256
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Signature algorithm: RSASSA-PKCS1-v1_5
#### MitraJcsEip191Signature2022
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Canonicalization algorithm: JCS
Hashing algorithm: KECCAK-256 (EIP-191)
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Signature algorithm: ECDSA (EIP-191)
#### MitraJcsEd25519Signature2022
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Canonicalization algorithm: JCS
Hashing algorithm: BLAKE2b-512
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Signature algorithm: EdDSA
## Profile extensions
### Cryptocurrency addresses
Cryptocurrency addresses are represented as `PropertyValue` attachments where `name` attribute is a currency symbol prefixed with `$`:
```json
{
"name": "$XMR",
"type": "PropertyValue",
"value": "8Ahza5RM4JQgtdqvpcF1U628NN5Q87eryXQad3Fy581YWTZU8o3EMbtScuioQZSkyNNEEE1Lkj2cSbG4VnVYCW5L1N4os5p"
}
```
### Identity proofs
Identity proofs are represented as attachments of `IdentityProof` type:
```json
{
"name": "<did>",
"type": "IdentityProof",
"signatureAlgorithm": "<proof-type>",
"signatureValue": "<proof>"
}
```
Supported proof types:
- EIP-191 (Ethereum personal signatures)
- [Minisign](https://jedisct1.github.io/minisign/)
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[FEP-c390](https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-c390.md) identity proofs are not supported yet.
## Account migrations
After registering an account its owner can upload the list of followers and start the migration process. The server then sends `Move` activity to each follower:
```json
{
"@context": [
"https://www.w3.org/ns/activitystreams"
],
"actor": "https://server2.com/users/alice",
"id": "https://server2.com/activities/00000000-0000-0000-0000-000000000001",
"object": "https://server1.com/users/alice",
"target": "https://server2.com/users/alice",
"to": [
"https://example.com/users/bob"
],
"type": "Move"
}
```
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Where `object` is an ID of old account and `target` is an ID of new account. Actors identified by `object` and `target` properties must have at least one identity key in common to be considered aliases. Upon receipt of such activity, actors that follow `object` should un-follow it and follow `target` instead.
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## Subscription events
Local actor profiles have `subscribers` property which points to the collection of actor's paid subscribers.
The `Add` activity is used to notify the subscriber about successful subscription payment. Upon receipt of this activity, the receiving server should add specified `object` to actors's `subscribers` collection (specified in `target` property):
```json
{
"@context": [
"https://www.w3.org/ns/activitystreams"
],
"actor": "https://example.com/users/alice",
"id": "https://example.com/activities/00000000-0000-0000-0000-000000000001",
"object": "https://example.com/users/bob",
"target": "https://example.com/users/alice/collections/subscribers",
"to": [
"https://example.com/users/bob"
],
"type": "Add"
}
```
The `Remove` activity is used to notify the subscriber about expired subscription. Upon receipt of this activity, the receiving server should remove specified `object` from actors's `subscribers` collection (specified in `target` property):
```json
{
"@context": [
"https://www.w3.org/ns/activitystreams"
],
"actor": "https://example.com/users/alice",
"id": "https://example.com/activities/00000000-0000-0000-0000-000000000002",
"object": "https://example.com/users/bob",
"target": "https://example.com/users/alice/collections/subscribers",
"to": [
"https://example.com/users/bob"
],
"type": "Remove"
}
```