Request for public keys only if LDAP attribute is set (#5816) (#5819)

* Update go-ldap dependency

* Request for public keys only if attribute is set

vendor/gopkg.in/ldap.v2/atomic_value_go13.go

@@ -0,0 +1,28 @@
+// +build !go1.4
+
+package ldap
+
+import (
+	"sync"
+)
+
+// This is a helper type that emulates the use of the "sync/atomic.Value"
+// struct that's available in Go 1.4 and up.
+type atomicValue struct {
+	value interface{}
+	lock  sync.RWMutex
+}
+
+func (av *atomicValue) Store(val interface{}) {
+	av.lock.Lock()
+	av.value = val
+	av.lock.Unlock()
+}
+
+func (av *atomicValue) Load() interface{} {
+	av.lock.RLock()
+	ret := av.value
+	av.lock.RUnlock()
+
+	return ret
+}