Refactor sign-in page and IAM service lifecycle

Redesign the sign-in page to show email/password form inline
with OIDC provider buttons (with vendor icons) instead of
separate pages. Extract OIDCProvider type to its own file.

Replace errgroup with sync.WaitGroup + WithCancelCause for
graceful shutdown in IAM services. Refactor garbage collectors
to use functional options and time.Ticker instead of
time.After to avoid repeated allocations.

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/iam/saml/service.go

@@ -24,6 +24,7 @@ import (
 	"fmt"
 	"net/url"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/crewjam/saml"
@@ -70,29 +71,25 @@ func NewService(
 }
 
 func (s *Service) Run(ctx context.Context) error {
-	gc := NewGarbageCollector(s.pg, DefaultGarbageCollectionInterval, s.logger)
+	wg := sync.WaitGroup{}
+	ctx, cancel := context.WithCancelCause(ctx)
+	defer cancel(context.Canceled)
 
-	gcCtx, stopGC := context.WithCancel(ctx)
-	defer stopGC()
-
-	errCh := make(chan error, 1)
-	go func() {
-		errCh <- gc.Run(gcCtx)
-	}()
-
-	select {
-	case <-ctx.Done():
-		stopGC()
-		<-errCh
-		return ctx.Err()
-	case err := <-errCh:
-		if err != nil {
-			s.logger.ErrorCtx(ctx, "saml garbage collector failed", log.Error(err))
-			return err
+	gcCtx, stopGC := context.WithCancel(context.WithoutCancel(ctx))
+	gc := NewGarbageCollector(s.pg, s.logger)
+	wg.Go(func() {
+		if err := gc.Run(gcCtx); err != nil {
+			cancel(fmt.Errorf("saml garbage collector crashed: %w", err))
 		}
+	})
 
-		return nil
-	}
+	<-ctx.Done()
+
+	stopGC()
+
+	wg.Wait()
+
+	return context.Cause(ctx)
 }
 
 func (s *Service) GenerateSpMetadata() ([]byte, error) {