rgw ldap: move conditional LDAPEngine init into it's ctor

rgw::auth::ExternalAuthStrategy defines an LDAPEngine in a
ctor-initializer list, making it too late to conditionally initialize
-it- in ExternalAuthStrategy's ctor.

Fixes: https://tracker.ceph.com/issues/24228

Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>
(cherry picked from commit 97e6c9d)

Conflicts:
	src/rgw/rgw_rest_s3.h : Added valid

src/rgw/rgw_auth_s3.h

@@ -79,8 +79,7 @@ class ExternalAuthStrategy : public rgw::auth::Strategy,
 
     }
 
-    if (cct->_conf->rgw_s3_auth_use_ldap &&
-        ! cct->_conf->rgw_ldap_uri.empty()) {
+    if (ldap_engine.valid()) {
       add_engine(Control::SUFFICIENT, ldap_engine);
     }
   }

src/rgw/rgw_rest_s3.cc

@@ -4059,6 +4059,11 @@ std::mutex rgw::auth::s3::LDAPEngine::mtx;
 
 void rgw::auth::s3::LDAPEngine::init(CephContext* const cct)
 {
+  if (! cct->_conf->rgw_s3_auth_use_ldap ||
+      ! cct->_conf->rgw_ldap_uri.empty()) {
+    return;
+  }
+
   if (! ldh) {
     std::lock_guard<std::mutex> lck(mtx);
     if (! ldh) {
@@ -4078,6 +4083,11 @@ void rgw::auth::s3::LDAPEngine::init(CephContext* const cct)
   }
 }
 
+bool rgw::auth::s3::LDAPEngine::valid() {
+  std::lock_guard<std::mutex> lck(mtx);
+  return (!!ldh);
+}
+
 rgw::auth::RemoteApplier::acl_strategy_t
 rgw::auth::s3::LDAPEngine::get_acl_strategy() const
 {

src/rgw/rgw_rest_s3.h

@@ -847,6 +847,8 @@ class LDAPEngine : public AWSEngine {
   const char* get_name() const noexcept override {
     return "rgw::auth::s3::LDAPEngine";
   }
+
+  static bool valid();
 };