feat(backend): start on fediverse auth support

backend/routes/auth/fedi_nodeinfo.go

@@ -0,0 +1,95 @@
+package auth
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+
+	"codeberg.org/u1f320/pronouns.cc/backend/server"
+	"emperror.dev/errors"
+)
+
+const errNoNodeinfoURL = errors.Sentinel("no valid nodeinfo rel found")
+
+// nodeinfo queries an instance's nodeinfo and returns the software name.
+func nodeinfo(ctx context.Context, instance string) (softwareName string, err error) {
+	req, err := http.NewRequestWithContext(ctx, "GET", "https://"+instance+"/.well-known/nodeinfo", nil)
+	if err != nil {
+		return "", errors.Wrap(err, "creating .well-known/nodeinfo request")
+	}
+	req.Header.Set("User-Agent", "pronouns.cc/"+server.Tag)
+	req.Header.Set("Accept", "application/json")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return "", errors.Wrap(err, "sending .well-known/nodeinfo request")
+	}
+	defer resp.Body.Close()
+
+	jb, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", errors.Wrap(err, "reading .well-known/nodeinfo response")
+	}
+
+	var wkr wellKnownResponse
+	err = json.Unmarshal(jb, &wkr)
+	if err != nil {
+		return "", errors.Wrap(err, "unmarshaling .well-known/nodeinfo response")
+	}
+
+	var nodeinfoURL string
+	for _, link := range wkr.Links {
+		if link.Rel == "http://nodeinfo.diaspora.software/ns/schema/2.0" {
+			nodeinfoURL = link.Href
+			break
+		}
+	}
+
+	if nodeinfoURL == "" {
+		return "", errNoNodeinfoURL
+	}
+
+	req, err = http.NewRequestWithContext(ctx, "GET", nodeinfoURL, nil)
+	if err != nil {
+		return "", errors.Wrap(err, "creating nodeinfo request")
+	}
+	req.Header.Set("User-Agent", "pronouns.cc/"+server.Tag)
+	req.Header.Set("Accept", "application/json")
+
+	resp, err = http.DefaultClient.Do(req)
+	if err != nil {
+		return "", errors.Wrap(err, "sending nodeinfo request")
+	}
+	defer resp.Body.Close()
+
+	jb, err = io.ReadAll(resp.Body)
+	if err != nil {
+		return "", errors.Wrap(err, "reading nodeinfo response")
+	}
+
+	var ni partialNodeinfo
+	err = json.Unmarshal(jb, &ni)
+	if err != nil {
+		return "", errors.Wrap(err, "unmarshaling nodeinfo response")
+	}
+
+	return ni.Software.Name, nil
+}
+
+type wellKnownResponse struct {
+	Links []wellKnownLink `json:"links"`
+}
+
+type wellKnownLink struct {
+	Rel  string `json:"rel"`
+	Href string `json:"href"`
+}
+
+type partialNodeinfo struct {
+	Software nodeinfoSoftware `json:"software"`
+}
+
+type nodeinfoSoftware struct {
+	Name string `json:"name"`
+}