Plugins: Add validation stage to plugin loader pipeline (#73053)

* first pass

* change validation signature

* err tracking

* fix

* undo golden

* 1 more

* fix

* adjust doc

* add test helper

* fix linter

pkg/plugins/manager/pipeline/validation/validation.go

@@ -0,0 +1,67 @@
+package validation
+
+import (
+	"context"
+	"errors"
+
+	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/plugins/config"
+	"github.com/grafana/grafana/pkg/plugins/log"
+)
+
+// Validator is responsible for the Validation stage of the plugin loader pipeline.
+type Validator interface {
+	Validate(ctx context.Context, ps []*plugins.Plugin) ([]*plugins.Plugin, error)
+}
+
+// ValidateFunc is the function used for the Validate step of the Validation stage.
+type ValidateFunc func(ctx context.Context, p *plugins.Plugin) error
+
+type Validate struct {
+	cfg           *config.Cfg
+	validateSteps []ValidateFunc
+	log           log.Logger
+}
+
+type Opts struct {
+	ValidateFuncs []ValidateFunc
+}
+
+// New returns a new Validation stage.
+func New(cfg *config.Cfg, opts Opts) *Validate {
+	if opts.ValidateFuncs == nil {
+		opts.ValidateFuncs = DefaultValidateFuncs(cfg)
+	}
+
+	return &Validate{
+		cfg:           cfg,
+		validateSteps: opts.ValidateFuncs,
+		log:           log.New("plugins.validation"),
+	}
+}
+
+// Validate will execute the Validate steps of the Validation stage.
+func (t *Validate) Validate(ctx context.Context, ps []*plugins.Plugin) ([]*plugins.Plugin, error) {
+	if len(t.validateSteps) == 0 {
+		return ps, nil
+	}
+
+	var err error
+	verifiedPlugins := make([]*plugins.Plugin, 0, len(ps))
+	for _, p := range ps {
+		stepFailed := false
+		for _, validate := range t.validateSteps {
+			err = validate(ctx, p)
+			if err != nil && !errors.Is(err, nil) {
+				stepFailed = true
+				t.log.Error("Plugin verification failed", "pluginID", p.ID, "err", err)
+				break
+			}
+		}
+		if !stepFailed {
+			verifiedPlugins = append(verifiedPlugins, p)
+		}
+	}
+
+	return verifiedPlugins, nil
+}