Authorization failure when indexing document with new mappings to alias.

index_to_alias_authorization

# Create an index called 'test', and an alias to it called 'test_alias'.
curl -XPUT -u elastic:<admin_password> http://localhost:9200/test -H 'Content-Type: application/json'
curl -XPOST -u elastic:<admin_password> http://localhost:9200/_aliases -H 'Content-Type: application/json' -d '{
    "actions" : [
        { "add" : { "index" : "test", "alias" : "test_alias" } }
    ]
}'

# Set ip a user called 'test_user' that is allowed to write to 'test_alias'.
curl -XPOST -u elastic:<admin_password> http://localhost:9200/_xpack/security/role/test_role -H 'Content-Type: application/json' -d '{
  "cluster": [
    "monitor"
  ],
  "indices": [
    {
      "names": [ "test_alias" ],
      "privileges": [ "write" ]
    }
  ]
}'

curl -XPOST -u elastic:1bMvr5d1rtChtrvQmQdd http://localhost:9200/_xpack/security/user/test_user -H 'Content-Type: application/json' -d '{
  "password" : "changeme",
  "roles" : [ "test_role" ]
}'

# Attempt to index a document with new mappings, and the below error occurs.
curl -XPOST -u test_user:changeme -H 'Content-Type: application/json' -XPOST localhost:9200/test_alias/doc/1?pretty -d '{
	"timestamp": "2018-05-11T12:00:00.000Z"
}'

> {
  "error" : {
    "root_cause" : [
      {
        "type" : "security_exception",
        "reason" : "action [indices:admin/mapping/put] is unauthorized for user [test_user]"
      }
    ],
    "type" : "security_exception",
    "reason" : "action [indices:admin/mapping/put] is unauthorized for user [test_user]"
  },
  "status" : 403
}

# Put mappings can successfully be called directly.
curl -u test_user:changeme -H 'Content-Type: application/json' -XPUT localhost:9200/test_alias/doc/_mapping -d '{
	"properties": {
		"timestamp":{"type":"date"}
	}
}'