runtime: context: support secret environment variables

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

plan/task/secretenv.go

@@ -0,0 +1,48 @@
+package task
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"cuelang.org/go/cue"
+	"github.com/rs/zerolog/log"
+	"go.dagger.io/dagger/compiler"
+	"go.dagger.io/dagger/plancontext"
+	"go.dagger.io/dagger/solver"
+)
+
+func init() {
+	Register("SecretEnv", func() Task { return &secretEnvTask{} })
+}
+
+type secretEnvTask struct {
+}
+
+func (c secretEnvTask) Run(ctx context.Context, pctx *plancontext.Context, _ solver.Solver, v *compiler.Value) (*compiler.Value, error) {
+	lg := log.Ctx(ctx)
+
+	var secretEnv struct {
+		Envvar string
+	}
+
+	if err := v.Decode(&secretEnv); err != nil {
+		return nil, err
+	}
+
+	lg.Debug().Str("envvar", secretEnv.Envvar).Msg("loading secret")
+
+	env := os.Getenv(secretEnv.Envvar)
+	if env == "" {
+		return nil, fmt.Errorf("environment variable %q not set", secretEnv.Envvar)
+	}
+	id := pctx.Secrets.Register(&plancontext.Secret{
+		PlainText: env,
+	})
+
+	out := compiler.NewValue()
+	if err := out.FillPath(cue.ParsePath("contents.id"), id); err != nil {
+		return nil, err
+	}
+	return out, nil
+}