Key Concepts

Let's take a look at some concepts and terminology that you need to know in order to follow the use cases.

WSO2 Cloud's user model

You can register to all WSO2 Public Cloud offerings (e.g., the Integration Cloud, the API Cloud) using a valid email address, and create multiple organizations under the same login. The system creates a unique tenant domain name for each organization you create. The user who creates an organization is assigned admin rights to it.

In WSO2 Public Cloud, users are authorized by their email addresses and are decoupled from organizations and tenant domains. This allows one user to be in multiple organizations (tenant domains) at the same time and log in to each organization using a single email address. If users are added to more than one organization, they are prompted to select the organization before logging in to its Cloud.

Diagram: WSO2 Cloud's user model

API Cloud components

WSO2 API Cloud consists of the API Publisher, Store, Gateway, Key Manager, Traffic Manager, and Analytics. The following diagram illustrates the components and the message flow between components:

• API Publisher: Enables complete API lifecycle governance—from creating to publishing, deprecating and retiring APIs. This component allows you to easily publish APIs, share documentation, and gather feedback on APIs, including their features, quality and usage.
• API Store: An intuitive consumer-like online store where,
  • API publishers can host and advertise their APIs.
  • API consumers can discover, evaluate, subscribe to and use secured, protected, authenticated APIs.
• API Gateway: Secures, protects, manages, and scales API calls. It is a simple API proxy that intercepts API requests and applies policies such as throttling and security. It also gathers API usage statistics.
• Key Manager: Handles all security and access token-related operations. The Gateway connects with the Key Manager to check the validity of OAuth tokens, subscriptions, and API invocations. 
  When a subscriber creates an application and generates an access token to the application using the API Store, the Store makes a call to the API Gateway, which in turn connects with the Key Manager to create an OAuth client and obtain an access token. Similarly, to validate a token, the API Gateway calls the Key Manager, which fetches and validates the token details from the database.
  The Key Manager also provides a token API to generate OAuth tokens that can be accessed via the Gateway. All tokens used for validation are based on the OAuth 2.0.0 protocol. Secure authorization of APIs is provided by the OAuth 2.0 standard for key management. The API Gateway supports API authentication with OAuth 2.0, and enables organizations to enforce rate limits and throttling policies.
• Traffic Manager: Helps to regulate API traffic, make APIs and applications available to consumers at different service levels, and secure APIs against security attacks. The Traffic Manager features a dynamic throttling engine to process throttling policies in real-time, including rate limiting of API requests.
• Analytics: The monitoring component provides a host of statistical graphs as well as an alerting mechanism on predetermined events.

Users and roles

The API Cloud offers distinct community roles that are applicable to most enterprises:

• APICloudPublisher: a publisher manages a set of APIs across the enterprise or business unit and controls the API lifecycle and subscription aspects. The publisher is also interested in usage patterns for APIs and has access to all API statistics.
• APICloudSubscriber: a subscriber uses the API store to discover APIs, read the documentation, and forums, rate/comment on the APIs, subscribes to APIs, obtain access tokens, and invoke the APIs.

API Lifecycle

An API is the published interface, while the Service is the implementation running in the backend. APIs have their own lifecycles that are independent of the backend Services they rely on. This lifecycle is exposed in the API publisher Web interface and is managed by the API publisher role.

The following stages are available in the default API lifecycle:

• CREATED:  API metadata is added to the API Store, but it is not deployed in the API gateway and therefore, is not visible to subscribers in the API Store.
• PROTOTYPED: the API is deployed and published in the API Store as a prototype. A prototype API is usually a mock implementation made public in order to get feedback about its usability. Users can invoke the API without a subscription.
• PUBLISHED: The API is visible in the API Store and available for subscription.
• DEPRECATED: When an API is deprecated, new subscriptions are disabled. But the API is still deployed in the Gateway and is available at runtime to existing subscribers. Existing subscribers can continue to use it as usual until the API is retired.
• RETIRED: The API is unpublished from the API gateway and deleted from the store.
• BLOCKED: Access to the API is temporarily blocked. Runtime calls are blocked and the API is not shown in the API Store anymore.

Applications

An application is a logical collection of APIs. An application is primarily used to decouple the consumer from the APIs. It allows you to :

• Generate and use a single key for multiple APIs
• Subscribe multiple times to a single API with different SLA levels

You subscribe to APIs through an application. Applications are available at different SLA levels and have application-level throttling tiers engaged in them. A throttling tier determines the maximum number of calls you can make to an API during a given period of time.

The API Cloud comes with a pre-created, default application. You can also create your own applications.

Access tokens

An access token is a simple string that is passed as an HTTP header of a request. For example, " Authorization: Bearer NtBQkXoKElu0H1a1fQ0DWfo6IX4a ." Access tokens authenticate API users and applications, and ensure better security (e.g., prevent  DoS attacks ). If a token that is passed with a request is invalid, the request is discarded in the first stage of processing. Access tokens work equally well for SOAP and REST calls.

There are two types of access tokens:

• User access tokens
• Application access tokens

User access tokens

Tokens to authenticate the final user of an API. User access tokens allow you to invoke an API even from a third-party application like a mobile app. You generate/renew a user access token by calling the Login API through a REST client. For more information, see Token API.

Application access tokens

Tokens to authenticate an application, which is a logical collection of APIs. They allow you to access all APIs associated with an application using a single token, and also subscribe multiple times to a single API with different SLA levels. Application access tokens leverage OAuth 2.0 to provide simple key management.

The steps below describe how to generate/renew application access tokens:

1. Log in to the API Store.

2. Click the Applications menu and then click the application to open it. For example,
   

3. Under the Production Keys tab, scroll down and click Regenerate.
   

Throttling

Throttling allows you to limit the number of successful hits to an API during a given period of time, typically in cases such as the following:

• To protect your APIs from common types of security attacks such as denial of service (DoS).
• To regulate traffic according to infrastructure availability.
• To make an API, application or a resource available to a consumer at different levels of service.

See Working with Throttling in the WSO2 API Manager documentation for detailed information about throttling, throttling limits, policies etc. 

API visibility and subscription

Visibility settings prevent certain user roles from viewing and modifying APIs created by another user role.

• Public: the API is visible to all users (registered and anonymous), and can be advertised in multiple stores (central and non-WSO2 stores).
• Visible to my domain: the API is visible to all users who are registered to the API's tenant domain.

• Restricted by Roles: The API is visible to its tenant domain and only to the user roles that you specify. Accepted roles are admin, publisher, subscriber, and appclouduser.
  

Given below is how visibility levels work for users in different roles:

• API creator and publisher roles can see all APIs in their tenant store even if you restrict access to them. This is because those roles have permission to view and edit all APIs in the API Publisher, and therefore, does not have to be restricted in the Store.
• Anonymous users can only see APIs that have visibility as Public.
• Registered users can see 
  • public APIs of all tenant domains   
  • all APIs in the registered user's tenant domain as long as the API is not restricted to a role that the user is assigned to

An API's visibility is directly related to the API's  subscription availability because you cannot subscribe to something you don't see in the Store. The diagram below depicts this relationship:

API resources

An API is made up of one or more resources. Each resource handles a particular type of request and is analogous to a method (function) in a larger API.
 

API resources accept following attributes:

<resource methods="POST GET" url-mapping="/state/town/*">
<resource methods="POST GET" uri-template="/{texas}/{houston}">

Once a request is accepted by a resource, it will be mediated through an in-sequence. Any response from the backend is handled through the out-sequence. Fault sequences are used to mediate errors that might occur in either sequence. The default in-sequence,out-sequence, and fault sequences are generated when the API is published.

Swagger API Console

WSO2 API Store provides an integrated Swagger UI, which is part of the Swagger project. You can use it for interactive API documentation and to invoke APIs.

Swagger is a 100% open source, standard, language-agnostic specification and a complete framework for describing, producing, consuming, and visualizing RESTful APIs, without the need of a proxy or third-party services. Swagger allows consumers to understand the capabilities of a remote service without accessing its source code and interact with the service with a minimal amount of implementation logic. Swagger helps describe services in the same way that interfaces describe lower-level programming code. 

The Swagger UI is a dependency-free collection of HTML, JavaScript, and CSS that dynamically generate documentation from a Swagger-compliant API. Swagger-compliant APIs give you interactive documentation, client SDK generation, and more discoverability.  The Swagger UI has JSON code and its UI facilitates easier code indentation, keyword highlighting and shows syntax errors on the fly. You can add resource parameters, summaries and descriptions to your APIs using the Swagger UI.

The API Publisher has integrated Swagger to facilitate simple, interactive API documentation and invocation. The documentation is given in a Swagger API definition, which is the JSON representation of the API that is created using the information provided at the time the API is created. The Swagger JSON files are saved in the registry.  You can edit the API definition using the Edit Swagger Definition button in the API Publisher.

Also, see the  Swagger 2.0 specification.

OAuth scopes

Scopes enable fine-grained access control to API resources based on user roles. You define scopes to an API's resource. When a user invokes the API, his/her OAuth 2 bearer token cannot grant access to any API resource beyond its associated scopes.

You can apply scopes to an API resource at the time the API is created or modified. In the API Publisher, click the API -> Add menu (to add a new API) or the Edit link next to an existing API. Then, navigate to the Manage tab and scroll down to see the Add Scopes button. A screen such as the following appears:

To illustrate the functionality of scopes, assume you have the following scopes attached to resources of an API: 

Assume that users named Tom and John are assigned the employee role and both the employee and manager roles respectively.  

Tom requests a token through the Token API as grant_type=password&username=tom&password=xxxx&scope=news_read news_write. However, as Tom is not in the manager role, he will only be granted a token bearing the news_read scope. The response from the Token API will be similar to the following:

"scope":"news_read",
"token_type":"bearer",
"expires_in":3299,
"refresh_token":"8579facb65d1d3eba74a395a2e78dd6",
"access_token":"eb51eff0b4d85cda1eb1d312c5b6a3b8"

Next, John requests a token as grant_type=password&username=john&password=john123&scope=news_read news_write. As John has both roles assigned, the token will bear both the requested scopes and the response will be similar to the following:

"scope":"news_read news_write", 
"token_type":"bearer", 
"expires_in":3299, 
"refresh_token":"4ca244fb321bd555bd3d555df39315",
"access_token":"42a377a0101877d1d9e29c5f30857e"

This means that Tom can only access the GET operation of the API while John can access both as he is assigned to both the employee and manager roles. If Tom tries to access the POST operation, there will be an HTTP 403 Forbidden error as follows:

<ams:fault xmlns:ams="http://wso2.org/apimanager/security">
   <ams:code>900910</ams:code>
      <ams:message>The access token does not allow you to access the requested resource</ams:message>
      <ams:description>Access failure for API: /orgnews, version: 1.0.0 with key: eb51eff0b4d85cda1eb1d312c5b6a3b8
   </ams:description>
</ams:fault>

Endpoints

An endpoint is a specific destination for a message such as an address, WSDL, a failover group, a load-balance group etc.

WSO2 API Manager has support for a range of different endpoint types, allowing the API Gateway to connect with advanced types of backends. It supports HTTP endpoints, URL endpoints (also termed as address endpoint), WSDL endpoints, Failover endpoints, Load-balanced endpoints. For more information about endpoints and how to add, edit or delete them, see the WSO2 ESB documentation.

Note the following:

• You can expose both REST and SOAP services to consumers through APIs.
• You cannot call backend services secured with OAuth through APIs created in the API Publisher. At the moment, you can call only services secured with username/password.

• The system reads gateway endpoints from the api-manager.xml file. When there are multiple gateway environments defined, it picks the gateway endpoint of the production environment. You can define both HTTP and HTTPS gateway endpoints as follows:

  <GatewayEndpoint>http://${carbon.local.ip}:${http.nio.port},https://${carbon.local.ip}:${https.nio.port}</GatewayEndpoint>

• If both types of endpoints are defined, the HTTPS endpoint will be picked as the server endpoint.

Sequences

The API Cloud has a default mediation flow that is executed in each API invocation. There are 3 default sequences engaged as in, out and fault.

Mediators

Sometimes, the backend implementation of a Web service does not exactly match your desired API design. In that case, you do various message transformations and orchestrate multiple backend services to achieve the design you want.

The API Cloud comes with a powerful mediation engine that can transform and orchestrate API calls on the fly. It is built on the WSO2 ESB and supports a variety of mediators that you can use as building blocks for your sequences. Given below is the list of mediators supported in the API Cloud:

Also, see the list of  WSO2 ESB Mediators. 

You can extend the API Gateway's default mediation flow to do custom mediation by providing an extension as a Synapse mediation sequence. You design all sequences using a tool like WSO2 Developer Studio and then store the sequence in the Gateway's registry. See Change the Default Mediation Flow of API Requests.

Response caching

Response caching stores the response messages per each API in a cache. It improves performance because the backend server does not have to process the same data for a request multiple times. To offset the risk of stale data in the cache, you can set a time period after which the cache is cleared periodically.   

Response caching is automatically disabled in the Cloud. You can enable it when creating a new API or editing an existing API. Go to the API's Manage tab in the API Publisher, and select Enable from the Response Caching drop-down list and give a time-out period.

Gateway caching

When an API call hits the API Gateway, the Gateway carries out security checks to verify if the token is valid. During these verifications, the API Gateway extracts parameters such as access token, API, and API version that are passed to it. Since all traffic to APIs goes through the API Gateway, this verification process can become an overhead if the API name, version, and other validation information are not cached. Therefore, caching is enabled at the Gateway by default.

When caching is enabled and a request hits the Gateway, it first populates the cached entry for a given token. If a cache entry does not exist in the cache, it calls the Key Manager server. This process is carried out using Web Service calls. Once the Key Manager server returns the validation information, it gets stored in the Gateway. Because the API Gateway issues a Web service call to the key manager server only if it does not have a cache entry, the number of Web service calls to the key manager server is reduced.

Admin Portal

WSO2 API Cloud provides you an admin portal which allows to perform administration on the Applications and APIs you have published. The left navigation bar of the admin portal directs to dfferent administration tasks as below.