PeerTube/server/core/middlewares/activitypub.ts

import { ActivityDelete, ActivityPubSignature, HttpStatusCode } from '@peertube/peertube-models'
import { isActorDeleteActivityValid } from '@server/helpers/custom-validators/activitypub/actor.js'
import { getAPId } from '@server/lib/activitypub/activity.js'
import { wrapWithSpanAndContext } from '@server/lib/opentelemetry/tracing.js'
import { NextFunction, Request, Response } from 'express'
import { logger } from '../helpers/logger.js'
import { isHTTPSignatureVerified, parseHTTPSignature } from '../helpers/peertube-crypto.js'
import { ACCEPT_HEADERS, ACTIVITY_PUB, HTTP_SIGNATURE } from '../initializers/constants.js'
import { getOrCreateAPActor, loadActorUrlOrGetFromWebfinger } from '../lib/activitypub/actors/index.js'

export async function checkSignature (req: Request, res: Response, next: NextFunction) {
  try {
    const httpSignatureChecked = await checkHttpSignature(req, res)
    if (httpSignatureChecked !== true) return

    const actor = res.locals.signature.actor

    // Forwarded activity
    const bodyActor = req.body.actor
    const bodyActorId = getAPId(bodyActor)
    if (bodyActorId && bodyActorId !== actor.url) {
      const jsonLDSignatureChecked = await checkJsonLDSignature(req, res)
      if (jsonLDSignatureChecked !== true) return
    }

    return next()
  } catch (err) {
    const activity: ActivityDelete = req.body
    if (isActorDeleteActivityValid(activity) && activity.object === activity.actor) {
      logger.debug('Handling signature error on actor delete activity', { err })
      return res.status(HttpStatusCode.NO_CONTENT_204).end()
    }

    logger.warn('Error in ActivityPub signature checker.', { err })
    return res.fail({
      status: HttpStatusCode.FORBIDDEN_403,
      message: 'ActivityPub signature could not be checked'
    })
  }
}

export function executeIfActivityPub (req: Request, res: Response, next: NextFunction) {
  const accepted = req.accepts(ACCEPT_HEADERS)
  if (accepted === false || ACTIVITY_PUB.POTENTIAL_ACCEPT_HEADERS.includes(accepted) === false) {
    // Bypass this route
    return next('route')
  }

  logger.debug('ActivityPub request for %s.', req.url)

  return next()
}

// ---------------------------------------------------------------------------
// Private
// ---------------------------------------------------------------------------

async function checkHttpSignature (req: Request, res: Response) {
  return wrapWithSpanAndContext('peertube.activitypub.checkHTTPSignature', async () => {
    // FIXME: compatibility with http-signature < v1.3
    const sig = req.headers[HTTP_SIGNATURE.HEADER_NAME] as string
    if (sig && sig.startsWith('Signature ') === true) req.headers[HTTP_SIGNATURE.HEADER_NAME] = sig.replace(/^Signature /, '')

    let parsed: any

    try {
      parsed = parseHTTPSignature(req, HTTP_SIGNATURE.CLOCK_SKEW_SECONDS)
    } catch (err) {
      logger.warn('Invalid signature because of exception in signature parser', { reqBody: req.body, err })

      res.fail({
        status: HttpStatusCode.FORBIDDEN_403,
        message: err.message
      })
      return false
    }

    const keyId = parsed.keyId
    if (!keyId) {
      res.fail({
        status: HttpStatusCode.FORBIDDEN_403,
        message: 'Invalid key ID',
        data: {
          keyId
        }
      })
      return false
    }

    logger.debug('Checking HTTP signature of actor %s...', keyId)

    let [ actorUrl ] = keyId.split('#')
    if (actorUrl.startsWith('acct:')) {
      actorUrl = await loadActorUrlOrGetFromWebfinger(actorUrl.replace(/^acct:/, ''))
    }

    const actor = await getOrCreateAPActor(actorUrl)

    const verified = isHTTPSignatureVerified(parsed, actor)
    if (verified !== true) {
      logger.warn('Signature from %s is invalid', actorUrl, { parsed })

      res.fail({
        status: HttpStatusCode.FORBIDDEN_403,
        message: 'Invalid signature',
        data: {
          actorUrl
        }
      })
      return false
    }

    res.locals.signature = { actor }
    return true
  })
}

async function checkJsonLDSignature (req: Request, res: Response) {
  // Lazy load the module as it's quite big with json.ld dependency
  const { compactJSONLDAndCheckSignature } = await import('../helpers/peertube-jsonld.js')

  return wrapWithSpanAndContext('peertube.activitypub.JSONLDSignature', async () => {
    const signatureObject: ActivityPubSignature = req.body.signature

    if (!signatureObject?.creator) {
      res.fail({
        status: HttpStatusCode.FORBIDDEN_403,
        message: 'Object and creator signature do not match'
      })
      return false
    }

    const [ creator ] = signatureObject.creator.split('#')

    logger.debug('Checking JsonLD signature of actor %s...', creator)

    const actor = await getOrCreateAPActor(creator)
    const verified = await compactJSONLDAndCheckSignature(actor, req)

    if (verified !== true) {
      logger.warn('Signature not verified.', req.body)

      res.fail({
        status: HttpStatusCode.FORBIDDEN_403,
        message: 'Signature could not be verified'
      })
      return false
    }

    res.locals.signature = { actor }
    return true
  })
}