gotosocial/internal/federation/authenticate.go

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/*
GoToSocial
Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package federation
import (
"context"
"crypto/x509"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
"net/http"
"net/url"
"strings"
"github.com/go-fed/activity/pub"
"github.com/go-fed/activity/streams"
"github.com/go-fed/activity/streams/vocab"
"github.com/go-fed/httpsig"
"github.com/superseriousbusiness/gotosocial/internal/db"
"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
)
/*
publicKeyer is BORROWED DIRECTLY FROM https://github.com/go-fed/apcore/blob/master/ap/util.go
Thank you @cj@mastodon.technology ! <3
*/
type publicKeyer interface {
GetW3IDSecurityV1PublicKey() vocab.W3IDSecurityV1PublicKeyProperty
}
/*
getPublicKeyFromResponse is adapted from https://github.com/go-fed/apcore/blob/master/ap/util.go
Thank you @cj@mastodon.technology ! <3
*/
func getPublicKeyFromResponse(c context.Context, b []byte, keyID *url.URL) (vocab.W3IDSecurityV1PublicKey, error) {
m := make(map[string]interface{})
if err := json.Unmarshal(b, &m); err != nil {
return nil, err
}
t, err := streams.ToType(c, m)
if err != nil {
return nil, err
}
pker, ok := t.(publicKeyer)
if !ok {
return nil, fmt.Errorf("ActivityStreams type cannot be converted to one known to have publicKey property: %T", t)
}
pkp := pker.GetW3IDSecurityV1PublicKey()
if pkp == nil {
return nil, errors.New("publicKey property is not provided")
}
var pkpFound vocab.W3IDSecurityV1PublicKey
for pkpIter := pkp.Begin(); pkpIter != pkp.End(); pkpIter = pkpIter.Next() {
if !pkpIter.IsW3IDSecurityV1PublicKey() {
continue
}
pkValue := pkpIter.Get()
var pkID *url.URL
pkID, err = pub.GetId(pkValue)
if err != nil {
return nil, err
}
if pkID.String() != keyID.String() {
continue
}
pkpFound = pkValue
break
}
if pkpFound == nil {
return nil, fmt.Errorf("cannot find publicKey with id: %s", keyID)
}
return pkpFound, nil
}
// AuthenticateFederatedRequest authenticates any kind of incoming federated request from a remote server. This includes things like
// GET requests for dereferencing our users or statuses etc, and POST requests for delivering new Activities. The function returns
// the URL of the owner of the public key used in the requesting http signature.
//
// Authenticate in this case is defined as making sure that the http request is actually signed by whoever claims
// to have signed it, by fetching the public key from the signature and checking it against the remote public key.
//
// To avoid making unnecessary http calls towards blocked domains, this function *does* bail early if an instance-level domain block exists
// for the request from the incoming domain. However, it does not check whether individual blocks exist between the requesting user or domain
// and the requested user: this should be done elsewhere.
//
// The provided username will be used to generate a transport for making remote requests/derefencing the public key ID of the request signature.
// Ideally you should pass in the username of the user *being requested*, so that the remote server can decide how to handle the request based on who's making it.
// Ie., if the request on this server is for https://example.org/users/some_username then you should pass in the username 'some_username'.
// The remote server will then know that this is the user making the dereferencing request, and they can decide to allow or deny the request depending on their settings.
//
// Note that it is also valid to pass in an empty string here, in which case the keys of the instance account will be used.
//
// Also note that this function *does not* dereference the remote account that the signature key is associated with.
// Other functions should use the returned URL to dereference the remote account, if required.
func (f *federator) AuthenticateFederatedRequest(requestedUsername string, r *http.Request) (*url.URL, error) {
var publicKey interface{}
var pkOwnerURI *url.URL
var err error
2021-05-09 18:34:27 +00:00
// set this extra field for signature validation
r.Header.Set("host", f.config.Host)
verifier, err := httpsig.NewVerifier(r)
if err != nil {
return nil, fmt.Errorf("could not create http sig verifier: %s", err)
}
// The key ID should be given in the signature so that we know where to fetch it from the remote server.
// This will be something like https://example.org/users/whatever_requesting_user#main-key
requestingPublicKeyID, err := url.Parse(verifier.KeyId())
if err != nil {
return nil, fmt.Errorf("could not parse key id into a url: %s", err)
}
// if the domain is blocked we want to make as few calls towards it as possible, so already bail here if that's the case!
blockedDomain, err := f.blockedDomain(requestingPublicKeyID.Host)
if err != nil {
return nil, fmt.Errorf("could not tell if domain %s was blocked or not: %s", requestingPublicKeyID.Host, err)
}
if blockedDomain {
return nil, fmt.Errorf("host %s was domain blocked, aborting auth", requestingPublicKeyID.Host)
}
requestingRemoteAccount := &gtsmodel.Account{}
requestingLocalAccount := &gtsmodel.Account{}
requestingHost := requestingPublicKeyID.Host
if strings.EqualFold(requestingHost, f.config.Host) {
// LOCAL ACCOUNT REQUEST
// the request is coming from INSIDE THE HOUSE so skip the remote dereferencing
if err := f.db.GetWhere([]db.Where{{Key: "public_key_uri", Value: requestingPublicKeyID.String()}}, requestingLocalAccount); err != nil {
return nil, fmt.Errorf("couldn't get local account with public key uri %s from the database: %s", requestingPublicKeyID.String(), err)
}
publicKey = requestingLocalAccount.PublicKey
pkOwnerURI, err = url.Parse(requestingLocalAccount.URI)
if err != nil {
return nil, fmt.Errorf("error parsing url %s: %s", requestingLocalAccount.URI, err)
}
} else if err := f.db.GetWhere([]db.Where{{Key: "public_key_uri", Value: requestingPublicKeyID.String()}}, requestingRemoteAccount); err == nil {
// REMOTE ACCOUNT REQUEST WITH KEY CACHED LOCALLY
// this is a remote account and we already have the public key for it so use that
publicKey = requestingRemoteAccount.PublicKey
pkOwnerURI, err = url.Parse(requestingRemoteAccount.URI)
if err != nil {
return nil, fmt.Errorf("error parsing url %s: %s", requestingRemoteAccount.URI, err)
}
} else {
// REMOTE ACCOUNT REQUEST WITHOUT KEY CACHED LOCALLY
// the request is remote and we don't have the public key yet,
// so we need to authenticate the request properly by dereferencing the remote key
transport, err := f.GetTransportForUser(requestedUsername)
if err != nil {
return nil, fmt.Errorf("transport err: %s", err)
}
// The actual http call to the remote server is made right here in the Dereference function.
b, err := transport.Dereference(context.Background(), requestingPublicKeyID)
if err != nil {
return nil, fmt.Errorf("error deferencing key %s: %s", requestingPublicKeyID.String(), err)
}
// if the key isn't in the response, we can't authenticate the request
requestingPublicKey, err := getPublicKeyFromResponse(context.Background(), b, requestingPublicKeyID)
if err != nil {
return nil, fmt.Errorf("error getting key %s from response %s: %s", requestingPublicKeyID.String(), string(b), err)
}
// we should be able to get the actual key embedded in the vocab.W3IDSecurityV1PublicKey
pkPemProp := requestingPublicKey.GetW3IDSecurityV1PublicKeyPem()
if pkPemProp == nil || !pkPemProp.IsXMLSchemaString() {
return nil, errors.New("publicKeyPem property is not provided or it is not embedded as a value")
}
// and decode the PEM so that we can parse it as a golang public key
pubKeyPem := pkPemProp.Get()
block, _ := pem.Decode([]byte(pubKeyPem))
if block == nil || block.Type != "PUBLIC KEY" {
return nil, errors.New("could not decode publicKeyPem to PUBLIC KEY pem block type")
}
publicKey, err = x509.ParsePKIXPublicKey(block.Bytes)
if err != nil {
return nil, fmt.Errorf("could not parse public key from block bytes: %s", err)
}
// all good! we just need the URI of the key owner to return
pkOwnerProp := requestingPublicKey.GetW3IDSecurityV1Owner()
if pkOwnerProp == nil || !pkOwnerProp.IsIRI() {
return nil, errors.New("publicKeyOwner property is not provided or it is not embedded as a value")
}
pkOwnerURI = pkOwnerProp.GetIRI()
}
if publicKey == nil {
return nil, errors.New("returned public key was empty")
}
// do the actual authentication here!
algo := httpsig.RSA_SHA256 // TODO: make this more robust
if err := verifier.Verify(publicKey, algo); err != nil {
return nil, fmt.Errorf("error verifying key %s: %s", requestingPublicKeyID.String(), err)
}
return pkOwnerURI, nil
}
func (f *federator) blockedDomain(host string) (bool, error) {
b := &gtsmodel.DomainBlock{}
err := f.db.GetWhere([]db.Where{{Key: "domain", Value: host, CaseInsensitive: true}}, b)
if err == nil {
// block exists
return true, nil
}
if _, ok := err.(db.ErrNoEntries); ok {
// there are no entries so there's no block
return false, nil
}
// there's an actual error
return false, err
}