Mint and verify short-lived RS256 user tokens.

ExApps sign after AppAPI auth; Microservices check a static public key or an OIDC issuer and forward the same bearer.

Co-authored-by: Cursor <cursoragent@cursor.com>

caller.go

@@ -0,0 +1,48 @@
+package usertoken
+
+import (
+	"context"
+	"errors"
+)
+
+// ErrUnauthorized is wrapped by every failed token check.
+// Startup and configuration failures do not wrap it.
+var ErrUnauthorized = errors.New("unauthorized")
+
+// Caller is the user a verified token names.
+// Groups is nil when the token omitted the claim, and non-nil (possibly empty)
+// when the claim was present.
+type Caller struct {
+	Subject  string
+	Username string
+	Groups   []string
+}
+
+type ctxKey int
+
+const (
+	ctxCaller ctxKey = iota
+	ctxBearer
+)
+
+// CallerFromContext returns the user [Auth.Middleware] stored.
+func CallerFromContext(ctx context.Context) (Caller, bool) {
+	c, ok := ctx.Value(ctxCaller).(Caller)
+	return c, ok
+}
+
+// BearerFromContext returns the raw JWT [Auth.Middleware] stored, without the
+// "Bearer " prefix. Outbound calls send "Bearer " plus this string.
+func BearerFromContext(ctx context.Context) (string, bool) {
+	s, ok := ctx.Value(ctxBearer).(string)
+	return s, ok
+}
+
+func withAuth(ctx context.Context, c Caller, raw string) context.Context {
+	ctx = context.WithValue(ctx, ctxCaller, c)
+	return context.WithValue(ctx, ctxBearer, raw)
+}
+
+func unauthorized(msg string) error {
+	return errors.Join(errors.New(msg), ErrUnauthorized)
+}