Fix broken certificate-authority-data with kubectl >= 1.8.0

changelogs/unreleased/fix-kubectl-180.yml

+---
+title: 'Kubernetes integration: ensure v1.8.0 compatibility'
+merge_request: 14635
+author:
+type: fixed

lib/gitlab/kubernetes.rb

@@ -113,7 +113,7 @@ module Gitlab
 
     def kubeconfig_embed_ca_pem(config, ca_pem)
       cluster = config.dig(:clusters, 0, :cluster)
-      cluster[:'certificate-authority-data'] = Base64.encode64(ca_pem)
+      cluster[:'certificate-authority-data'] = Base64.strict_encode64(ca_pem)
     end
   end
 end

spec/fixtures/config/kubeconfig.yml

@@ -4,7 +4,7 @@ clusters:
 - name: gitlab-deploy
   cluster:
     server: https://kube.domain.com
-    certificate-authority-data: "UEVN\n"
+    certificate-authority-data: "UEVN"
 contexts:
 - name: gitlab-deploy
   context:

spec/models/project_services/kubernetes_service_spec.rb

@@ -208,7 +208,7 @@ describe KubernetesService, :use_clean_rails_memory_store_caching do
       config.dig('users', 0, 'user')['token'] = 'token'
       config.dig('contexts', 0, 'context')['namespace'] = namespace
       config.dig('clusters', 0, 'cluster')['certificate-authority-data'] =
-        Base64.encode64('CA PEM DATA')
+        Base64.strict_encode64('CA PEM DATA')
 
       YAML.dump(config)
     end