[DOCS] Format the authenticate API (elastic/x-pack-elasticsearch#2572)
[DOCS] Format the authenticate API (elastic/x-pack-elasticsearch#2572)

Original commit: elastic/x-pack-elasticsearch@bc486dc6be01eb0298a99fe10b4282f311e93faf

gingerwizard/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,gfyoung/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,gfyoung/elasticsearch,GlenRSmith/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,HonzaKral/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,gfyoung/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,gfyoung/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,coding0011/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,HonzaKral/elasticsearch,gfyoung/elasticsearch,nknize/elasticsearch,robin13/elasticsearch