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service-client.md

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Factory+ service client

import { ServiceClient } from "@amrc-factoryplus/utilities";

This class provides support for the process of consuming Factory+ services as a client.

All methods (should) use a Debug object for logging, allowing logging to be configured via the VERBOSE environment variable.

In order to successfully use GSSAPI authentication (required, for now) the environment variable KRB5CCNAME must be set to point to a Kerberos ccache containing a valid TGT we can use to fetch service tickets. The Docker images contain a utility called k5start which can be useful to obtain a TGT and keep it up to date.

Constructor

fplus = await new ServiceClient({...}).init();

Build a new service client. Before using the object, call and await the init method to complete setup. Options to the constructor (all are optional, though some interfaces require certain options) are:

Option Meaning
root_principal Kerberos principal which overrides permission checks.
permission_group Permission group for ACL checks.
directory_url URL to the Directory.
username Optional Username for Basic Authentication.
password Optional Password for Basic Authentication. 
await fplus.init();

Completes setup of the client object. Returns the client object.

Service discovery

Service discovery starts with the URL of the Directory as supplied to the constructor. This URL forms a trust root; the Directory will be contacted over HTTP at the URL given, its identity verified by GSSAPI (and perhaps TLS), and the URLs returned trusted to provide the services they are listed for.

service_url

url = await fplus.service_url(service);

Returns the first URL from service_urls, or undefined. Should be considered deprecated, as services may have multiple URLs and this method cannot perform liveness testing.

service_urls

urls = await fplus.service_urls(service);

Accepts a service function UUID. Returns a list of URLs to potential providers of that service. These should be tried in order until one can be successfully contacted.

set_service_discovery

fplus.set_service_discovery(locator);

Install a function used to locate service URLs instead of querying the Directory. Used internally by the Directory.

set_service_url

fplus.set_service_url(service, url);

Preset a URL for the given service.

Service HTTP requests

fetch

response = await fplus.fetch({ service, url, ...opts });

Discover a HTTP URL for a service and make a HTTP request. Responses will be properly cached according to the headers returned by the server. By default, this will perform a GSSAPI fetch for a token, if necessary, and cache tokens for later requests to the same service. The service will perform a Basic Authentication instead if ServiceClient is supplied with credentials.

Returns a Response object according to the Fetch spec. In the case of an error fetching a URL or a token the status property of the response will be 0.

Accepts all options acceptable to fetch. Also accepts and requires:

Option Meaning
service The UUID of the service to contact.
url The URL, relative to the service URL from discovery.

Authentication service

The Authentication service interface uses the root_principal and permission_group parameters to the constructor. The first specifies a Kerberos principal name that will override all ACL checks; if an ACL check is made for that principal then it will always return success. The second specifies the UUID of the permission group to request when fetching ACLs from the Auth service; see the service documentation for more details.

check_acl

ok = await fplus.check_acl(principal, permission, target, wild);

Checks if the given principal has the given permission on the given target. Fetches permissions for the permission_group specified to the constructor, so the requested permission must be in that group.

The principal is specified either as a string containing a Kerberos principal name (for backwards compatability), or as an object containing a single property, kerberos or uuid, with a value as appropriate. (More principal types may be accepted in the future.) The permission and target are UUIDs.

The wild parameter is an optional boolean. If true, then a null UUID in the target of an ACE will be treated as a wildcard matching any target. Note: the null UUID must be in the target of the ACE in the auth database, not in the target parameter passed to the method. If false or unspecified the target must match exactly.

fetch_acl

check = await fplus.fetch_acl(principal, group);

Fetches the ACL for the given principal and permission group and returns a function to check a permission for a particular target. The principal is specified as above. The returned function is used as follows, where the parameters are as above.

ok = check(permission, target, wild);

resolve_principal

uuid = fplus.resolve_principal(query);

Locate a principal and return its UUID. The query must currently be an object with a single key kerberos to search for a principal by Kerberos principal name, but this may be extended in future to support other principal identifiers. Returns null if the principal is not found.

ConfigDB service

fetch_configdb

json = await fplus.fetch_configdb(app, obj);

Fetch an entry from the ConfigDB. The parameters are the UUIDs of the application and object for the entry to fetch. Returns the config entry parsed from JSON, or undefined.

MQTT service

MQTT 5 supports extended authentication mechanisms, but no mechanisms have been defined on the standards track. Factory+ defines a mechanism supporting GSSAPI authentication, as follows:

  • The authentication method is GSSAPI.
  • The client shall call GSS_Init_sec_context with a NULL input_token and send the resulting output_token as authentication data in the CONNECT packet.
  • The server shall call GSS_Accept_sec_context with the received token and:
    • If the context indicates authentication failure, optionally send a CONNACK with Reason Code indicating failure and close the connection.
    • If the context is now complete, send the final token back as the authentication data in a CONNACK packet indicating success.
    • If the context is not complete, send the output token back in an AUTH packet with Reason Code 24 (Continue Authentication).
  • The client shall pass the received token to GSS_Init_sec_context with the same context as before. Then:
    • If the context indicates authentication failure, optionally send an appropriate DISCONNECT and close the connection.
    • If the server sent a CONNACK, and the client context is now complete, authentication is successful.
    • If the server sent a CONNACK, and the client context is not now complete, authentication has failed. Optionally send DISCONNECT and close the connection.
    • If the server sent an AUTH, the client shall send the output token in an AUTH packet with Reason Code 24.
  • Client and server shall keep sending AUTH packets until the server receives a complete context and sends CONNACK, or until authentication fails.

The Factory+ implementation of this currently only accepts Kerberos GSSAPI tokens and expects a single-round exchange with no AUTH packets. The service identifier for an MQTT service principal should be mqtt.

mqtt_client

mqtt = await fplus.mqtt_client(opts);

The MQTT service opens a connection using GSSAPI authentication, or uses Basic Authentication if ServiceClient is supplied with credentials. The service can be supplied with an endpoint under otps.host, or it will attempt to perform service discovery for a MQTT broker. The options are as documented for the mqtt npm module except where they are overridden to support GSSAPI auth. The protocol version will always be MQTT 5.

The returned object is a Client object from the mqtt module, but the connect event is required to complete the authentication exchange. Do not add additional handlers to this event; instead use the authenticated event, which will only fire once authentication is successfully completed. This event will also be passed the CONNACK message, should you need it.

Returns null if discovery fails. Set an explicit service URL for UUIDs.Service.MQTT if you don't want discovery via the Directory.