Remote instance dereferencing (#70)

Remote instances are now dereferenced when they post to an inbox on a GtS instance.

    Dereferencing will be done first by checking the /api/v1/instance endpoint of an instance.
    If that doesn't work, /.well-known/nodeinfo will be checked.
    If that doesn't work, only a minimal representation of the instance will be stored.

A new field was added to the Instance database model. To create it:

alter table instances add column contact_account_username text;

6 files changed, 300 insertions, 212 deletions

diff --git a/internal/federation/util.go b/internal/federation/authenticate.go
index 9ec0770f6..c4183144b 100644
--- a/internal/federation/util.go
+++ b/internal/federation/authenticate.go
@@ -35,8 +35,6 @@ import (
 	"github.com/go-fed/httpsig"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
-	"github.com/superseriousbusiness/gotosocial/internal/transport"
-	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
 )
 
 /*
@@ -99,11 +97,14 @@ func getPublicKeyFromResponse(c context.Context, b []byte, keyID *url.URL) (voca
 
 // 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 http signature.
+// the URL of the owner of the public key used in the requesting http signature.
 //
-// Authenticate in this case is defined as just 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. This function
-// *does not* check whether the request is authorized, only whether it's authentic.
+// 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.
@@ -114,7 +115,12 @@ func getPublicKeyFromResponse(c context.Context, b []byte, keyID *url.URL) (voca
 //
 // 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(username string, r *http.Request) (*url.URL, error) {
+func (f *federator) AuthenticateFederatedRequest(requestedUsername string, r *http.Request) (*url.URL, error) {
+
+	var publicKey interface{}
+	var pkOwnerURI *url.URL
+	var err error
+
 	// set this extra field for signature validation
 	r.Header.Set("host", f.config.Host)
 
@@ -130,11 +136,19 @@ func (f *federator) AuthenticateFederatedRequest(username string, r *http.Reques
 		return nil, fmt.Errorf("could not parse key id into a url: %s", err)
 	}
 
-	var publicKey interface{}
-	var pkOwnerURI *url.URL
+	// 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{}
-	if strings.EqualFold(requestingPublicKeyID.Host, f.config.Host) {
+	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 {
@@ -157,7 +171,7 @@ func (f *federator) AuthenticateFederatedRequest(username string, r *http.Reques
 		// 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(username)
+		transport, err := f.GetTransportForUser(requestedUsername)
 		if err != nil {
 			return nil, fmt.Errorf("transport err: %s", err)
 		}
@@ -212,154 +226,19 @@ func (f *federator) AuthenticateFederatedRequest(username string, r *http.Reques
 	return pkOwnerURI, nil
 }
 
-func (f *federator) DereferenceRemoteAccount(username string, remoteAccountID *url.URL) (typeutils.Accountable, error) {
-	f.startHandshake(username, remoteAccountID)
-	defer f.stopHandshake(username, remoteAccountID)
-
-	transport, err := f.GetTransportForUser(username)
-	if err != nil {
-		return nil, fmt.Errorf("transport err: %s", err)
-	}
-
-	b, err := transport.Dereference(context.Background(), remoteAccountID)
-	if err != nil {
-		return nil, fmt.Errorf("error deferencing %s: %s", remoteAccountID.String(), err)
-	}
-
-	m := make(map[string]interface{})
-	if err := json.Unmarshal(b, &m); err != nil {
-		return nil, fmt.Errorf("error unmarshalling bytes into json: %s", err)
-	}
-
-	t, err := streams.ToType(context.Background(), m)
-	if err != nil {
-		return nil, fmt.Errorf("error resolving json into ap vocab type: %s", err)
-	}
-
-	switch t.GetTypeName() {
-	case string(gtsmodel.ActivityStreamsPerson):
-		p, ok := t.(vocab.ActivityStreamsPerson)
-		if !ok {
-			return nil, errors.New("error resolving type as activitystreams person")
-		}
-		return p, nil
-	case string(gtsmodel.ActivityStreamsApplication):
-		p, ok := t.(vocab.ActivityStreamsApplication)
-		if !ok {
-			return nil, errors.New("error resolving type as activitystreams application")
-		}
-		return p, nil
-	case string(gtsmodel.ActivityStreamsService):
-		p, ok := t.(vocab.ActivityStreamsService)
-		if !ok {
-			return nil, errors.New("error resolving type as activitystreams service")
-		}
-		return p, nil
-	}
-
-	return nil, fmt.Errorf("type name %s not supported", t.GetTypeName())
-}
-
-func (f *federator) DereferenceRemoteStatus(username string, remoteStatusID *url.URL) (typeutils.Statusable, error) {
-	transport, err := f.GetTransportForUser(username)
-	if err != nil {
-		return nil, fmt.Errorf("transport err: %s", err)
-	}
-
-	b, err := transport.Dereference(context.Background(), remoteStatusID)
-	if err != nil {
-		return nil, fmt.Errorf("error deferencing %s: %s", remoteStatusID.String(), err)
-	}
-
-	m := make(map[string]interface{})
-	if err := json.Unmarshal(b, &m); err != nil {
-		return nil, fmt.Errorf("error unmarshalling bytes into json: %s", err)
-	}
-
-	t, err := streams.ToType(context.Background(), m)
-	if err != nil {
-		return nil, fmt.Errorf("error resolving json into ap vocab type: %s", err)
-	}
-
-	// Article, Document, Image, Video, Note, Page, Event, Place, Mention, Profile
-	switch t.GetTypeName() {
-	case gtsmodel.ActivityStreamsArticle:
-		p, ok := t.(vocab.ActivityStreamsArticle)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsArticle")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsDocument:
-		p, ok := t.(vocab.ActivityStreamsDocument)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsDocument")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsImage:
-		p, ok := t.(vocab.ActivityStreamsImage)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsImage")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsVideo:
-		p, ok := t.(vocab.ActivityStreamsVideo)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsVideo")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsNote:
-		p, ok := t.(vocab.ActivityStreamsNote)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsNote")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsPage:
-		p, ok := t.(vocab.ActivityStreamsPage)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsPage")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsEvent:
-		p, ok := t.(vocab.ActivityStreamsEvent)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsEvent")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsPlace:
-		p, ok := t.(vocab.ActivityStreamsPlace)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsPlace")
-		}
-		return p, nil
-	case gtsmodel.ActivityStreamsProfile:
-		p, ok := t.(vocab.ActivityStreamsProfile)
-		if !ok {
-			return nil, errors.New("error resolving type as ActivityStreamsProfile")
-		}
-		return p, 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
 	}
 
-	return nil, fmt.Errorf("type name %s not supported", t.GetTypeName())
-}
-
-func (f *federator) GetTransportForUser(username string) (transport.Transport, error) {
-	// We need an account to use to create a transport for dereferecing the signature.
-	// If a username has been given, we can fetch the account with that username and use it.
-	// Otherwise, we can take the instance account and use those credentials to make the request.
-	ourAccount := &gtsmodel.Account{}
-	var u string
-	if username == "" {
-		u = f.config.Host
-	} else {
-		u = username
-	}
-	if err := f.db.GetLocalAccountByUsername(u, ourAccount); err != nil {
-		return nil, fmt.Errorf("error getting account %s from db: %s", username, err)
+	if _, ok := err.(db.ErrNoEntries); ok {
+		// there are no entries so there's no block
+		return false, nil
 	}
 
-	transport, err := f.transportController.NewTransport(ourAccount.PublicKeyURI, ourAccount.PrivateKey)
-	if err != nil {
-		return nil, fmt.Errorf("error creating transport for user %s: %s", username, err)
-	}
-	return transport, nil
+	// there's an actual error
+	return false, err
 }
diff --git a/internal/federation/commonbehavior.go b/internal/federation/commonbehavior.go
index fab9ce112..29eb9b6f3 100644
--- a/internal/federation/commonbehavior.go
+++ b/internal/federation/commonbehavior.go
@@ -20,15 +20,10 @@ package federation
 
 import (
 	"context"
-	"fmt"
 	"net/http"
-	"net/url"
 
-	"github.com/go-fed/activity/pub"
 	"github.com/go-fed/activity/streams"
 	"github.com/go-fed/activity/streams/vocab"
-	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
-	"github.com/superseriousbusiness/gotosocial/internal/util"
 )
 
 /*
@@ -101,53 +96,3 @@ func (f *federator) GetOutbox(ctx context.Context, r *http.Request) (vocab.Activ
 	// the CLIENT API, not through the federation API, so we just do nothing here.
 	return streams.NewActivityStreamsOrderedCollectionPage(), nil
 }
-
-// NewTransport returns a new Transport on behalf of a specific actor.
-//
-// The actorBoxIRI will be either the inbox or outbox of an actor who is
-// attempting to do the dereferencing or delivery. Any authentication
-// scheme applied on the request must be based on this actor. The
-// request must contain some sort of credential of the user, such as a
-// HTTP Signature.
-//
-// The gofedAgent passed in should be used by the Transport
-// implementation in the User-Agent, as well as the application-specific
-// user agent string. The gofedAgent will indicate this library's use as
-// well as the library's version number.
-//
-// Any server-wide rate-limiting that needs to occur should happen in a
-// Transport implementation. This factory function allows this to be
-// created, so peer servers are not DOS'd.
-//
-// Any retry logic should also be handled by the Transport
-// implementation.
-//
-// Note that the library will not maintain a long-lived pointer to the
-// returned Transport so that any private credentials are able to be
-// garbage collected.
-func (f *federator) NewTransport(ctx context.Context, actorBoxIRI *url.URL, gofedAgent string) (pub.Transport, error) {
-
-	var username string
-	var err error
-
-	if util.IsInboxPath(actorBoxIRI) {
-		username, err = util.ParseInboxPath(actorBoxIRI)
-		if err != nil {
-			return nil, fmt.Errorf("couldn't parse path %s as an inbox: %s", actorBoxIRI.String(), err)
-		}
-	} else if util.IsOutboxPath(actorBoxIRI) {
-		username, err = util.ParseOutboxPath(actorBoxIRI)
-		if err != nil {
-			return nil, fmt.Errorf("couldn't parse path %s as an outbox: %s", actorBoxIRI.String(), err)
-		}
-	} else {
-		return nil, fmt.Errorf("id %s was neither an inbox path nor an outbox path", actorBoxIRI.String())
-	}
-
-	account := &gtsmodel.Account{}
-	if err := f.db.GetLocalAccountByUsername(username, account); err != nil {
-		return nil, fmt.Errorf("error getting account with username %s from the db: %s", username, err)
-	}
-
-	return f.transportController.NewTransport(account.PublicKeyURI, account.PrivateKey)
-}
diff --git a/internal/federation/dereference.go b/internal/federation/dereference.go
new file mode 100644
index 000000000..111c0b977
--- /dev/null
+++ b/internal/federation/dereference.go
@@ -0,0 +1,153 @@
+package federation
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+
+	"github.com/go-fed/activity/streams"
+	"github.com/go-fed/activity/streams/vocab"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
+)
+
+func (f *federator) DereferenceRemoteAccount(username string, remoteAccountID *url.URL) (typeutils.Accountable, error) {
+	f.startHandshake(username, remoteAccountID)
+	defer f.stopHandshake(username, remoteAccountID)
+
+	transport, err := f.GetTransportForUser(username)
+	if err != nil {
+		return nil, fmt.Errorf("transport err: %s", err)
+	}
+
+	b, err := transport.Dereference(context.Background(), remoteAccountID)
+	if err != nil {
+		return nil, fmt.Errorf("error deferencing %s: %s", remoteAccountID.String(), err)
+	}
+
+	m := make(map[string]interface{})
+	if err := json.Unmarshal(b, &m); err != nil {
+		return nil, fmt.Errorf("error unmarshalling bytes into json: %s", err)
+	}
+
+	t, err := streams.ToType(context.Background(), m)
+	if err != nil {
+		return nil, fmt.Errorf("error resolving json into ap vocab type: %s", err)
+	}
+
+	switch t.GetTypeName() {
+	case string(gtsmodel.ActivityStreamsPerson):
+		p, ok := t.(vocab.ActivityStreamsPerson)
+		if !ok {
+			return nil, errors.New("error resolving type as activitystreams person")
+		}
+		return p, nil
+	case string(gtsmodel.ActivityStreamsApplication):
+		p, ok := t.(vocab.ActivityStreamsApplication)
+		if !ok {
+			return nil, errors.New("error resolving type as activitystreams application")
+		}
+		return p, nil
+	case string(gtsmodel.ActivityStreamsService):
+		p, ok := t.(vocab.ActivityStreamsService)
+		if !ok {
+			return nil, errors.New("error resolving type as activitystreams service")
+		}
+		return p, nil
+	}
+
+	return nil, fmt.Errorf("type name %s not supported", t.GetTypeName())
+}
+
+func (f *federator) DereferenceRemoteStatus(username string, remoteStatusID *url.URL) (typeutils.Statusable, error) {
+	transport, err := f.GetTransportForUser(username)
+	if err != nil {
+		return nil, fmt.Errorf("transport err: %s", err)
+	}
+
+	b, err := transport.Dereference(context.Background(), remoteStatusID)
+	if err != nil {
+		return nil, fmt.Errorf("error deferencing %s: %s", remoteStatusID.String(), err)
+	}
+
+	m := make(map[string]interface{})
+	if err := json.Unmarshal(b, &m); err != nil {
+		return nil, fmt.Errorf("error unmarshalling bytes into json: %s", err)
+	}
+
+	t, err := streams.ToType(context.Background(), m)
+	if err != nil {
+		return nil, fmt.Errorf("error resolving json into ap vocab type: %s", err)
+	}
+
+	// Article, Document, Image, Video, Note, Page, Event, Place, Mention, Profile
+	switch t.GetTypeName() {
+	case gtsmodel.ActivityStreamsArticle:
+		p, ok := t.(vocab.ActivityStreamsArticle)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsArticle")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsDocument:
+		p, ok := t.(vocab.ActivityStreamsDocument)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsDocument")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsImage:
+		p, ok := t.(vocab.ActivityStreamsImage)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsImage")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsVideo:
+		p, ok := t.(vocab.ActivityStreamsVideo)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsVideo")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsNote:
+		p, ok := t.(vocab.ActivityStreamsNote)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsNote")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsPage:
+		p, ok := t.(vocab.ActivityStreamsPage)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsPage")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsEvent:
+		p, ok := t.(vocab.ActivityStreamsEvent)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsEvent")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsPlace:
+		p, ok := t.(vocab.ActivityStreamsPlace)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsPlace")
+		}
+		return p, nil
+	case gtsmodel.ActivityStreamsProfile:
+		p, ok := t.(vocab.ActivityStreamsProfile)
+		if !ok {
+			return nil, errors.New("error resolving type as ActivityStreamsProfile")
+		}
+		return p, nil
+	}
+
+	return nil, fmt.Errorf("type name %s not supported", t.GetTypeName())
+}
+
+func (f *federator) DereferenceRemoteInstance(username string, remoteInstanceURI *url.URL) (*gtsmodel.Instance, error) {
+	transport, err := f.GetTransportForUser(username)
+	if err != nil {
+		return nil, fmt.Errorf("transport err: %s", err)
+	}
+
+	return transport.DereferenceInstance(context.Background(), remoteInstanceURI)
+}
diff --git a/internal/federation/federatingprotocol.go b/internal/federation/federatingprotocol.go
index 8784c32e2..bd540af2c 100644
--- a/internal/federation/federatingprotocol.go
+++ b/internal/federation/federatingprotocol.go
@@ -125,6 +125,29 @@ func (f *federator) AuthenticatePostInbox(ctx context.Context, w http.ResponseWr
 		return ctx, false, fmt.Errorf("not authenticated: %s", err)
 	}
 
+	// authentication has passed, so add an instance entry for this instance if it hasn't been done already
+	i := &gtsmodel.Instance{}
+	if err := f.db.GetWhere([]db.Where{{Key: "domain", Value: publicKeyOwnerURI.Host, CaseInsensitive: true}}, i); err != nil {
+		if _, ok := err.(db.ErrNoEntries); !ok {
+			// there's been an actual error
+			return ctx, false, fmt.Errorf("error getting requesting account with public key id %s: %s", publicKeyOwnerURI.String(), err)
+		}
+
+		// we don't have an entry for this instance yet so dereference it
+		i, err = f.DereferenceRemoteInstance(username, &url.URL{
+			Scheme: publicKeyOwnerURI.Scheme,
+			Host:   publicKeyOwnerURI.Host,
+		})
+		if err != nil {
+			return nil, false, fmt.Errorf("could not dereference new remote instance %s during AuthenticatePostInbox: %s", publicKeyOwnerURI.Host, err)
+		}
+
+		// and put it in the db
+		if err := f.db.Put(i); err != nil {
+			return nil, false, fmt.Errorf("error inserting newly dereferenced instance %s: %s", publicKeyOwnerURI.Host, err)
+		}
+	}
+
 	requestingAccount := &gtsmodel.Account{}
 	if err := f.db.GetWhere([]db.Where{{Key: "uri", Value: publicKeyOwnerURI.String()}}, requestingAccount); err != nil {
 		// there's been a proper error so return it
diff --git a/internal/federation/federator.go b/internal/federation/federator.go
index 2ee01697f..0c6b54e37 100644
--- a/internal/federation/federator.go
+++ b/internal/federation/federator.go
@@ -28,6 +28,7 @@ import (
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/federation/federatingdb"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/transport"
 	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
 )
@@ -50,6 +51,9 @@ type Federator interface {
 	// DereferenceRemoteStatus can be used to get the representation of a remote status, based on its ID (which is a URI).
 	// The given username will be used to create a transport for making outgoing requests. See the implementation for more detailed comments.
 	DereferenceRemoteStatus(username string, remoteStatusID *url.URL) (typeutils.Statusable, error)
+	// DereferenceRemoteInstance takes the URL of a remote instance, and a username (optional) to spin up a transport with. It then
+	// does its damnedest to get some kind of information back about the instance, trying /api/v1/instance, then /.well-known/nodeinfo
+	DereferenceRemoteInstance(username string, remoteInstanceURI *url.URL) (*gtsmodel.Instance, error)
 	// GetTransportForUser returns a new transport initialized with the key credentials belonging to the given username.
 	// This can be used for making signed http requests.
 	//
diff --git a/internal/federation/transport.go b/internal/federation/transport.go
new file mode 100644
index 000000000..a92f66d25
--- /dev/null
+++ b/internal/federation/transport.go
@@ -0,0 +1,84 @@
+package federation
+
+import (
+	"context"
+	"fmt"
+	"net/url"
+
+	"github.com/go-fed/activity/pub"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/transport"
+	"github.com/superseriousbusiness/gotosocial/internal/util"
+)
+
+// NewTransport returns a new Transport on behalf of a specific actor.
+//
+// The actorBoxIRI will be either the inbox or outbox of an actor who is
+// attempting to do the dereferencing or delivery. Any authentication
+// scheme applied on the request must be based on this actor. The
+// request must contain some sort of credential of the user, such as a
+// HTTP Signature.
+//
+// The gofedAgent passed in should be used by the Transport
+// implementation in the User-Agent, as well as the application-specific
+// user agent string. The gofedAgent will indicate this library's use as
+// well as the library's version number.
+//
+// Any server-wide rate-limiting that needs to occur should happen in a
+// Transport implementation. This factory function allows this to be
+// created, so peer servers are not DOS'd.
+//
+// Any retry logic should also be handled by the Transport
+// implementation.
+//
+// Note that the library will not maintain a long-lived pointer to the
+// returned Transport so that any private credentials are able to be
+// garbage collected.
+func (f *federator) NewTransport(ctx context.Context, actorBoxIRI *url.URL, gofedAgent string) (pub.Transport, error) {
+
+	var username string
+	var err error
+
+	if util.IsInboxPath(actorBoxIRI) {
+		username, err = util.ParseInboxPath(actorBoxIRI)
+		if err != nil {
+			return nil, fmt.Errorf("couldn't parse path %s as an inbox: %s", actorBoxIRI.String(), err)
+		}
+	} else if util.IsOutboxPath(actorBoxIRI) {
+		username, err = util.ParseOutboxPath(actorBoxIRI)
+		if err != nil {
+			return nil, fmt.Errorf("couldn't parse path %s as an outbox: %s", actorBoxIRI.String(), err)
+		}
+	} else {
+		return nil, fmt.Errorf("id %s was neither an inbox path nor an outbox path", actorBoxIRI.String())
+	}
+
+	account := &gtsmodel.Account{}
+	if err := f.db.GetLocalAccountByUsername(username, account); err != nil {
+		return nil, fmt.Errorf("error getting account with username %s from the db: %s", username, err)
+	}
+
+	return f.transportController.NewTransport(account.PublicKeyURI, account.PrivateKey)
+}
+
+func (f *federator) GetTransportForUser(username string) (transport.Transport, error) {
+	// We need an account to use to create a transport for dereferecing something.
+	// If a username has been given, we can fetch the account with that username and use it.
+	// Otherwise, we can take the instance account and use those credentials to make the request.
+	ourAccount := &gtsmodel.Account{}
+	var u string
+	if username == "" {
+		u = f.config.Host
+	} else {
+		u = username
+	}
+	if err := f.db.GetLocalAccountByUsername(u, ourAccount); err != nil {
+		return nil, fmt.Errorf("error getting account %s from db: %s", username, err)
+	}
+
+	transport, err := f.transportController.NewTransport(ourAccount.PublicKeyURI, ourAccount.PrivateKey)
+	if err != nil {
+		return nil, fmt.Errorf("error creating transport for user %s: %s", username, err)
+	}
+	return transport, nil
+}