[bugfix] httpclient not signing subsequent redirect requests (#2798)

* move http request signing to transport

* actually hook up the http roundtripper ...

* add code comments for the new gtscontext functions

internal/gtscontext/context.go

@@ -19,6 +19,7 @@ package gtscontext
 
 import (
 	"context"
+	"net/http"
 	"net/url"
 
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
@@ -42,6 +43,7 @@ const (
 	httpSigKey
 	httpSigPubKeyIDKey
 	dryRunKey
+	httpClientSignFnKey
 )
 
 // DryRun returns whether the "dryrun" context key has been set. This can be
@@ -127,6 +129,19 @@ func SetOtherIRIs(ctx context.Context, iris []*url.URL) context.Context {
 	return context.WithValue(ctx, otherIRIsKey, iris)
 }
 
+// HTTPClientSignFunc returns an httpclient signing function for the current client
+// request context. This can be used to resign a request as calling transport's user.
+func HTTPClientSignFunc(ctx context.Context) func(*http.Request) error {
+	fn, _ := ctx.Value(httpClientSignFnKey).(func(*http.Request) error)
+	return fn
+}
+
+// SetHTTPClientSignFunc stores the given httpclient signing function and returns the wrapped
+// context. See HTTPClientSignFunc() for further information on the signing function value.
+func SetHTTPClientSignFunc(ctx context.Context, fn func(*http.Request) error) context.Context {
+	return context.WithValue(ctx, httpClientSignFnKey, fn)
+}
+
 // HTTPSignatureVerifier returns an http signature verifier for the current ActivityPub
 // request chain. This verifier can be called to authenticate the current request.
 func HTTPSignatureVerifier(ctx context.Context) httpsig.VerifierWithOptions {