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https://github.com/digitalbazaar/ezcap

An opinionated Authorization Capabilities client
https://github.com/digitalbazaar/ezcap

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An opinionated Authorization Capabilities client

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README 

          
# ezcap



[![Node.js CI](https://github.com/digitalbazaar/ezcap/workflows/Node.js%20CI/badge.svg)](https://github.com/digitalbazaar/ezcap/actions?query=workflow%3A%22Node.js+CI%22)



> An easy to use, opinionated Authorization Capabilities (zcap) client library

> for the browser and Node.js.



## Table of Contents



- [Background](#background)

- [Security](#security)

- [Install](#install)

- [Usage](#usage)

- [API Reference](#api-reference)

- [Contribute](#contribute)

- [Commercial Support](#commercial-support)

- [License](#license)



## Background



This library provides a client that browser and node.js applications can use to

interact with HTTP servers protected by zcap-based authorization. The library

is configured with secure and sensible defaults to help developers get started

quickly and ensure that their client code is production-ready.



## Security



The security characteristics of this library are largely influenced by design

decisions made by client and server software. For clients, implementers should

pay particular attention to secure private key management. For servers, security

characteristics are largely dependent on how carefully the server manages zcap

registrations, zcap invocations, and zcap delegations. Bugs or failures related

to client key management, or server zcap validity checking will lead to security

failures. It is imperative that implementers audit their implementations,

preferably via parties other than the implementer.



## Install



- Browsers and Node.js 14+ are supported.

- [Web Crypto API][] required. Older browsers and Node.js 14 must use a

  polyfill.



To install from NPM:



```

npm install @digitalbazaar/ezcap

```



To install locally (for development):



```

git clone https://github.com/digitalbazaar/ezcap.git

cd ezcap

npm install

```



## Usage



* [Creating a Client](#creating-a-client)

* [Reading with a Root Capability](#reading-with-a-root-capability)

* [Writing with a Root Capability](#writing-with-a-root-capability)

* [Delegating a Capability](#delegating-a-capability)

* [Reading with a Delegated Capability](#reading-with-a-delegated-capability)

* [Writing with a Delegated Capability](#writing-with-a-delegated-capability)

* [Requesting with a Root Capability](#requesting-with-a-root-capability)

* [Requesting with a Delegated Capability](#requesting-with-a-delegated-capability)



### Creating a Client



Creating a zcap client involves generating cryptographic key material and then

using that key material to instantiate a client designed to operate on a

specific base URL.



```js

import {ZcapClient} from '@digitalbazaar/ezcap';

import * as didKey from '@digitalbazaar/did-method-key';

import {Ed25519Signature2020} from '@digitalbazaar/ed25519-signature-2020';

const didKeyDriver = didKey.driver();



// generate a DID Document and set of key pairs

const {didDocument, keyPairs} = await didKeyDriver.generate();



// create a new zcap client using the generated cryptographic material

const zcapClient = new ZcapClient({

  didDocument, keyPairs, SuiteClass: Ed25519Signature2020

});

```



### Reading with a Root Capability



Reading data from a URL using a capability is performed in a way that is

very similar to using a regular HTTP client to perform an HTTP GET. Using

a root capability means that your client has been directly authorized to access

the URL, usually because it created the resource that is being accessed.

The term "root" means that your client is the "root of authority".



```js

const url = 'https://zcap.example/my-account/items';



// reading a URL using a zcap will result in an HTTP Response

const response = await zcapClient.read({url});



// retrieve the JSON data

const items = await response.json();

```



### Writing with a Root Capability



Writing data to URL using a capability is performed in a way that is

very similar to using a regular HTTP client to perform an HTTP POST. Using

a root capability means that your client has been directly authorized to

modify the resource at the URL, usually because it created the resource that is

being written to. The term "root" means that your client is the "root of

authority". In the example below, the server most likely registered the

client as being the root authority for the `/my-account` path on the server.



```js

const url = 'https://zcap.example/my-account/items';

const item = {label: 'Widget'};



// writing a URL using a zcap will result in an HTTP Response

const response = await zcapClient.write({url, json: item});



// process the response appropriately

const writtenItem = await response.json();

```



### Delegating a Capability



Delegating a capability consists of the client authorizing another entity to

use the capability. The example below uses a DID as the target for the

delegation. The returned `delegatedCapability` would need to be transmitted

to the entity identified by the delegation target so that they can use it

to access the resource.



```js

const invocationTarget = 'https://zcap.example/my-account/items';

const controller =

  'did:key:z6MkpTHR8VNsBxYAAWHut2Geadd9jSwuBV8xRoAnwWsdvktH';

const allowedActions = ['read'];

const delegatedCapability = zcapClient.delegate(

  {invocationTarget, controller, allowedActions});

```



### Reading with a Delegated Capability



Reading with a delegated capability is similar to reading with a root

capability. The only difference is that the delegated capability needs to be

retrieved from somewhere using application-specific code and then passed

to the `read` method.



```js

const url = 'https://zcap.example/my-account/items/123';

// defined by your code

const capability = await getCapabilityFromDatabase({url});



// reading a URL using a zcap will result in an HTTP Response; the

// `invocationTarget` from the capability provides the URL if one is not

// specified; if a URL is specified, the capability's invocation target

// MUST be a RESTful prefix of or equivalent to the URL

const response = await zcapClient.read({capability});



// retrieve the JSON data

const items = await response.json();

```



### Writing with a Delegated Capability



Writing with a delegated capability is similar to writing with a root

capability. The only difference is that the delegated capability needs to be

retrieved from somewhere using application-specific code and then passed

to the `write` method.



```js

const item = {label: 'Widget'};

const url = 'https://zcap.example/my-account/items';

// defined by your code

const capability = await getCapabilityFromDatabase({url});



// writing a URL using a zcap will result in an HTTP Response; the

// `invocationTarget` from the capability provides the URL if one is not

// specified; if a URL is specified, the capability's invocation target

// MUST be a RESTful prefix of or equivalent to the URL

const response = await zcapClient.write({capability, json: item});



// process the response appropriately

const writtenItem = await response.json();

```



### Requesting with a Root Capability



In the event that the server API does not operate using HTTP GET and HTTP POST,

it is possible to create a zcap client request that uses other HTTP verbs. This

is done by specifying the HTTP `method` to use.



```js

const url = 'https://zcap.example/my-account/items';

const item = {count: 12};



// send a request to a URL by invoking a capability

const response = await zcapClient.request({url, method: 'patch', json: item});



// process the response appropriately

const updatedItem = await response.json();

```



### Requesting with a Delegated Capability



Performing an HTTP request with a delegated capability is similar to

doing the same with a root capability. The only difference is that the

delegated capability needs to be retrieved from somewhere using application-specific code and then passed to the `request` method.



```js

const item = {count: 12};

const url = 'https://zcap.example/my-account/items/123';

// defined by your code

const capability = await getCapabilityFromDatabase({url});



// invoking a capability against a URL will result in an HTTP Response; the

// `invocationTarget` from the capability provides the URL if one is not

// specified; if a URL is specified, the capability's invocation target

// MUST be a RESTful prefix of or equivalent to the URL

const response = await zcapClient.request(

  {capability, method: 'patch', json: item});



// process the response appropriately

const updatedItem = await response.json();

```



## API Reference



The ezcap approach is opinionated in order to make using zcaps a pleasant

experience for developers. To do this, it makes two fundamental assumptions

regarding the systems it interacts with:



* The systems are HTTP-based and REST-ful in nature.

* The REST-ful systems center around reading and writing resources.



If these assumptions do not apply to your system, the

[zcap](https://github.com/digitalbazaar/zcap) library might

be a better, albeit more complex, solution for you.



Looking at each of these core assumptions more closely will help explain how designing systems to these constraints make it much easier to think about

zcaps. Let's take a look at the first assumption:



> The systems are HTTP-based and REST-ful in nature.



Many modern systems tend to have HTTP-based interfaces that are REST-ful in

nature. That typically means that most resource URLs are organized by namespaces, collections, and items:

`///`. In practice,

this tends to manifest itself as URLs that look like

`/my-account/things/1`. The ezcap approach maps the authorization model

in a 1-to-1 way to the URL. Following along with the example, the root

capability would then be `/my-account`, which you will typically create and

have access to. You can then take that root capability and delegate access

to things like `/my-account/things` to let entities you trust modify the

`things` collection. You can also choose to be more specific and only

delegate to `/my-account/things/1` to really lock down access. ezcap attempts

to keep things very simple by mapping URL hierarchy to authorization scope.



Now, let's examine the second assumption that makes things easier:



> The REST-ful systems center around reading and writing resources.



There is an incredible amount of flexibility that zcaps provide. You can

define a variety of actions: read, write, bounce, atomicSwap, start, etc.

However, all that flexibility adds complexity and one of the goals of ezcap

is to reduce complexity to the point where the solution is good enough for

80% of the use cases. A large amount of REST-ful interactions tend to

revolve around reading and writing collections and the items in those

collections. For this reason, there are only two actions that are exposed

by default in ezcap: read and write. Keeping the number of actions to a

bare minimum has allowed implementers to achieve very complex use cases with

very simple code.



These are the two assumptions that ezcap makes and with those two assumptions,

80% of all use cases we've encountered are covered.



## Classes





ZcapClient







## Functions







getCapabilitySigners(options) ⇒ object





Retrieves the first set of capability invocation and delegation signers

associated with the didDocument from the keyPairs.






generateZcapUri(options) ⇒ string





Generate a zcap URI given a root capability URL or a delegated flag.







## Typedefs







HttpsAgent : object





An object that manages connection persistence and reuse for HTTPS requests.






LinkedDataSignatureSuiteClass : object





An class that can be instantiated to create a suite capable of generating a

Linked Data Signature. Its constructor must receive a signer instance

that includes .sign() function and id and controller properties.










## ZcapClient

**Kind**: global class  



* [ZcapClient](#ZcapClient)

    * [new ZcapClient(options)](#new_ZcapClient_new)

    * [.delegate(options)](#ZcapClient+delegate) ⇒ Promise.<object>

    * [.request(options)](#ZcapClient+request) ⇒ Promise.<object>

    * [.read(options)](#ZcapClient+read) ⇒ Promise.<object>

    * [.write(options)](#ZcapClient+write) ⇒ Promise.<object>






### new ZcapClient(options)

Creates a new ZcapClient instance that can be used to perform

requests against HTTP URLs that are authorized via

Authorization Capabilities (ZCAPs).



**Returns**: [ZcapClient](#ZcapClient) - - The new ZcapClient instance.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| options.SuiteClass | [LinkedDataSignatureSuiteClass](#LinkedDataSignatureSuiteClass) | The LD   signature suite class to use to sign requests and delegations. |

| [options.didDocument] | object | A DID Document that contains   `capabilityInvocation` and `capabilityDelegation` verification   relationships; `didDocument` and `keyPairs`, or `invocationSigner` and   `delegationSigner` must be provided in order to invoke or delegate   zcaps, respectively. |

| [options.keyPairs] | Map | A map of key pairs associated with   `didDocument` indexed by key pair; `didDocument` and `keyPairs`, or   `invocationSigner` and `delegationSigner` must be provided in order to    invoke or delegate zcaps, respectively. |

| [options.delegationSigner] | object | An object with a   `.sign()` function and `id` and `controller` properties that will be   used for delegating zcaps; `delegationSigner` or `didDocument` and   `keyPairs` must be provided to delegate zcaps. |

| [options.invocationSigner] | object | An object with a   `.sign()` function and `id` and `controller` properties that will be   used for signing requests; `invocationSigner` or `didDocument` and   `keyPairs` must be provided to invoke zcaps. |

| [options.agent] | [HttpsAgent](#HttpsAgent) | An optional HttpsAgent to use to   when performing HTTPS requests. |

| [options.defaultHeaders] | object | The optional default HTTP   headers to include in every invocation request. |

| [options.documentLoader] | function | Optional document loader   to load suite-related contexts. If none is provided, one will be   auto-generated if the suite class expresses its required context. |






### zcapClient.delegate(options) ⇒ Promise.<object>

Delegates an Authorization Capability to a target delegate.



**Kind**: instance method of [ZcapClient](#ZcapClient)  

**Returns**: Promise.<object> - - A promise that resolves to a delegated

  capability.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| [options.capability] | object | The parent capability to   delegate; must be an object if it is a delegated zcap, can be a string   if it is a root zcap but then `invocationTarget` must be specified; if   not specified, this will be auto-generated as a root zcap for the given   `invocationTarget`. |

| options.controller | string | The URL identifying the entity to   delegate to, i.e., the party that will control the new zcap. |

| [options.invocationTarget] | string | Optional invocation target   to use when narrowing a `capability`'s existing invocationTarget.   Default is to use `capability.invocationTarget`, provided that   `capability` is an object. |

| [options.expires] | string \| Date | Optional expiration value   for the delegation. Default is 5 minutes after `Date.now()`. |

| [options.allowedActions] | string \| Array | Optional list of allowed   actions or string specifying allowed delegated action. Default: [] -   delegate all actions. |






### zcapClient.request(options) ⇒ Promise.<object>

Performs an HTTP request given an Authorization Capability (zcap) and/or

a target URL. If no URL is given, the invocation target from the

capability will be used. If a capability is given as a string, it MUST

be a root capability. If both a capability and a URL are given, then

the capability's invocation target MUST be a RESTful prefix of or

equivalent to the URL.



**Kind**: instance method of [ZcapClient](#ZcapClient)  

**Returns**: Promise.<object> - - A promise that resolves to an HTTP response.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| [options.url] | string | The URL to invoke the   Authorization Capability against; if not provided, a `capability` must   be provided instead. |

| [options.capability] | string \| object | The capability to invoke at   the given URL. Default: generate root capability from options.url. |

| [options.method] | string | The HTTP method to use when accessing   the resource. Default: 'get'. |

| [options.action] | string | The capability action that is being   invoked. Default: 'read'. |

| [options.headers] | object | The additional headers to sign and   send along with the HTTP request. Default: {}. |

| options.json | object | The JSON object, if any, to send with the   request. |






### zcapClient.read(options) ⇒ Promise.<object>

Convenience function that invokes an Authorization Capability against a

given URL to perform a read operation.



**Kind**: instance method of [ZcapClient](#ZcapClient)  

**Returns**: Promise.<object> - - A promise that resolves to an HTTP response.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| options.url | string | The URL to invoke the   Authorization Capability against. |

| options.headers | object | The additional headers to sign and   send along with the HTTP request. |

| [options.capability] | string | The capability to invoke at the   given URL. Default: generate root capability from options.url. |






### zcapClient.write(options) ⇒ Promise.<object>

Convenience function that invokes an Authorization Capability against a

given URL to perform a write operation.



**Kind**: instance method of [ZcapClient](#ZcapClient)  

**Returns**: Promise.<object> - - A promise that resolves to an HTTP response.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| options.url | string | The URL to invoke the   Authorization Capability against. |

| options.json | object | The JSON object, if any, to send with the   request. |

| [options.headers] | object | The additional headers to sign and   send along with the HTTP request. |

| [options.capability] | string | The capability to invoke at the   given URL. Default: generate root capability from options.url. |






## getCapabilitySigners(options) ⇒ object

Retrieves the first set of capability invocation and delegation signers

associated with the `didDocument` from the `keyPairs`.



**Kind**: global function  

**Returns**: object - - A valid `invocationSigner` and `delegationSigner`

  associated with the didDocument.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| options.didDocument | string | A DID Document containing   verification relationships for capability invocation and delegation. |

| options.keyPairs | string | A map containing keypairs indexed by   key ID. |






## generateZcapUri(options) ⇒ string

Generate a zcap URI given a root capability URL or a delegated flag.



**Kind**: global function  

**Returns**: string - - A zcap URI.  



| Param | Type | Description |

| --- | --- | --- |

| options | object | The options to use. |

| [options.url] | string | Optional URL identifying the root capability. |






## HttpsAgent : object

An object that manages connection persistence and reuse for HTTPS requests.



**Kind**: global typedef  

**See**: https://nodejs.org/api/https.html#https_class_https_agent  




## LinkedDataSignatureSuiteClass : object

An class that can be instantiated to create a suite capable of generating a

Linked Data Signature. Its constructor must receive a `signer` instance

that includes `.sign()` function and `id` and `controller` properties.



**Kind**: global typedef  



## Contribute



See [the contribute file](https://github.com/digitalbazaar/bedrock/blob/master/CONTRIBUTING.md)! PRs accepted.



If editing the README.md, please follow the

[standard-readme](https://github.com/RichardLitt/standard-readme) specification.



## Commercial Support



Commercial support for this library is available upon request from

Digital Bazaar: support@digitalbazaar.com



## License



[New BSD License (3-clause)](LICENSE) © Digital Bazaar



[Web Crypto API]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Crypto_API