Add OAuth client branding for trust centers

Serve CIMD logos from dedicated endpoints, expose client metadata
branding through GraphQL, and resolve branding from OAuth clients.

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

pkg/iam/oauth2/client_branding.go

@@ -0,0 +1,67 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package oauth2
+
+import (
+	"context"
+	"errors"
+
+	"go.probo.inc/probo/pkg/coredata"
+)
+
+type ClientBranding struct {
+	Name      string
+	ClientURL *string
+	LogoURL   *string
+}
+
+func (s *Service) ClientBranding(ctx context.Context, clientIDRaw string) (*ClientBranding, error) {
+	if clientIDRaw == "" {
+		return nil, nil
+	}
+
+	client, err := s.resolveClient(ctx, nil, clientIDRaw)
+	if err != nil {
+		if _, ok := errors.AsType[*OAuth2Error](err); ok {
+			return nil, nil
+		}
+
+		return nil, err
+	}
+
+	return ClientBrandingFromClient(client), nil
+}
+
+func ClientBrandingFromClient(client *coredata.OAuth2Client) *ClientBranding {
+	if client == nil || client.ClientName == "" {
+		return nil
+	}
+
+	branding := &ClientBranding{
+		Name: client.ClientName,
+	}
+
+	if client.ClientURI != nil {
+		clientURL := client.ClientURI.String()
+		branding.ClientURL = &clientURL
+	}
+
+	if client.LogoURI != nil {
+		logoURL := client.LogoURI.String()
+		branding.LogoURL = &logoURL
+	}
+
+	return branding
+}