实体/资源上的RESTful API授权？ [英] RESTful API authorization on entities/resources?

问题描述

我正在使用具有非常复杂的访问控制规则的系统中的API。通常，需要复杂的SQL查询来确定用户是否具有对特定资源的读取或写入访问权限。这会导致我们的客户端应用程序出现很多复杂性和冗余，因为它们必须了解所有这些规则才能确定是否向用户显示每个对象的CRUD选项。

我的目标是减少客户端的许多复杂性，并将所有复杂的逻辑包含在API中。这样，当确保UI仅向用户提供有效选项时，针对我们的API编写的新客户端应用程序可以避免重新实现复杂的访问规则逻辑。

我不确定最好的方法是什么。我正在考虑两个不同的选项，但是我不知道是否有更好或更标准的方法可以向API调用者公开通用访问信息。

选项1

当调用方对资源实体或资源实体进行GET请求时，每个返回的实体都会返回 _allowed_actions 附加的字段，该字段是允许调用者对该实体执行的一系列操作。例如，请求 Listing 对象可能会导致以下响应。

GET / listing / 5

  {
 id：5，
地址： 123 Foo Street，
城市：纽约，
州：纽约，
价格：457000，
状态：待定，
 _allowed_actions：[读取，更新，删除] 
} 
  

仍然不确定如何与客户端建立联系，他们是否有权使用此方法创建资源实体的实例，但是客户端可能只需要保持足够的了解即可权限结构自行决定。创建实例周围的访问规则通常比READ / UPDATE / DELETE访问规则复杂，因此看起来并不算太糟。

选项2

创建一个元API，客户端可以对其进行请求，以确定他们可以对每种资源执行哪些操作。例如，检查客户端可以使用列表进行什么操作：

GET / access-query / listing / 5

  {
 allowed_actions：[ READ， UPDATE， DELETE] 
} 
  

并检查总体上允许使用哪些选项，包括CREATE：

获取/访问查询/列表

  {
 allowed_actions：[读取，创建，更新，删除] 
} 
  

这种方法的好处在于，它使调用者可以全面了解自己可以使用通用方法对每种资源执行的操作。这样，客户就不必了解创建列表所需的 create_listing权限和非试用用户状态。他们可以简单地提前查询这些信息。

这种方法的缺点是增加了请求数量。现在，他们不再需要客户端了解权限逻辑，而是必须查询一次以确定他们可以做什么，然后再查询一次。

我不这些方法中的任何一种都不特别在意，但目前我只能提出它们。

解决方案

您正在寻找的是细粒度的外部授权：

p>

• 细粒度：您要创建授权策略，该策略考虑多个参数或属性以及客户端（请求者）与客户端之间的关系目标实体，例如


• 已被外部化：您希望将业务逻辑与授权逻辑分离。在您的问题中，您抱怨代码和SQL语句变得越来越复杂。这是未将业务逻辑与授权逻辑明确分开的直接结果。

有一个模型称为基于属性的访问控制（ABAC） ），该方法定义了一种用于细化外部授权的方法。美国国家标准与技术研究院（NIST）已发布了

用于Eclipse的ALFA插件-编写XACML策略的免费工具。

XACML开发人员社区

XACML既有供应商实现，也有开源实现：

• Axiomatics是一种提供.NET和Java XACML实现的供应商解决方案


• SunXACML是长期存在的开源Java XACML实施

HTH，
David。

I am working on an API in a system that has very complex access control rules. Often times there are complex SQL queries required to determine if a user has read or write access to a particular resource. This causes a lot of complexity and redundancy in our client applications as they have to know all these rules in order to determine whether to present the user with CRUD options for each object.

My goal is to reduce much of the complexity on the client side and house all the complex logic in the API. This way new client applications written against our API can avoid re-implementing the complex access rule logic on their side when ensuring that the UI only presents valid options to the user.

I am not sure what the best way is to handle this. I'm considering two different options but I don't know if there is a better or more standard way to expose generic access information to callers of an API.

Option 1

When a caller makes a GET request on a resource entity or collection of them, every returned entity will return an _allowed_actions field attached, which is an array of actions the caller is allowed to perform on that entity. For example, requesting a Listing object may result in the following response.

GET /listing/5

{
 "id": 5,
 "address": "123 Foo Street",
 "city": "New York",
 "state": "New York",
 "price": 457000,
 "status": "pending",
 "_allowed_actions": ["READ", "UPDATE", "DELETE"]
}

Still unsure how to relate to clients whether they have the authority to create instances of a resource entity using this method, but perhaps the client will simply need to maintain enough understanding of the permission structure to determine this on its own. The access rules around creating instances are typically less complex than the READ/UPDATE/DELETE access rules so that doesn't seem too bad.

Option 2

Create a meta-API, which clients can make requests to in order to determine what actions they can perform on each resource. For example, checking what the client can do with a listing:

GET /access-query/listing/5

{
 "allowed_actions": ["READ", "UPDATE","DELETE"]
}

And checking what options are allowed for listings in general, including CREATE:

GET /access-query/listing

{
 "allowed_actions": ["READ", "CREATE", "UPDATE", "DELETE"]
}

The benefit of this approach is that it allows callers to have a full understanding of what they can do on every resource in a generic way. This way clients wouldn't have to understand that the "create_listing" permission AND a non-probationary user status are required required in order to create listings. They can simply query for this information ahead of time.

The downside to this approach is that it increases the amount of requests. Rather than require clients to have an understanding of the permissions logic, they now have to query once to determine what they can do and a second time to do it.

I don't particularly care for either of these methods but they're all I can come up with at the moment. Is there a better way to go about this?

解决方案

What you are looking for is fine-grained, externalized authorization:

• fine-grained: you want to create authorization policies that take into account multiple parameters or attributes and possibly relationships between the client (the requestor) and the targeted entity e.g. a listing in your case.
• externalized: you want to decouple the business logic from the authorization logic. In your question you complain about how complex the code and the SQL statements are becoming. This is a direct consequence of not clearly separating business logic from authorization logic.

There is a model called attribute-based access control (ABAC) that defines an approach to fine-grained externalized authorization. NIST, the National Institute of Standards and Technology, has produced a report on ABAC which you can read online.

OASIS, the organization for the advancement of structured information standards, has defined a standard called XACML (eXtensible Access Control Markup Language) to implement ABAC.

XACML brings you:

• an architecture as illustrated below
  • The policy enforcement point (PEP) intercepts your API calls. It protects your API, inspects the messages and sends an authorization request to the policy decision point (PDP).
  • The policy decision point (PDP) evaluates incoming authorization requests from the PEP against a set of authorization policies written in XACML. The PDP eventually reaches a Permit or Deny decision. To reach decisions it may need to look up additional attribute values from databases, web services, LDAP, or files. These are called policy information points in the architecture.
• a policy language: the XACML policy language is attribute-based which means it uses attributes to define what can be allowed and what is not. For instance, you could define rules such as:
  • a real estate agent can see all the listings if and only if the listing location == the agent location
  • a real estate agent can edit a listing if and only if he/she owns the listing
  • a real estate agent can close a listing if and only if the listing's item is sold and if and only if the agent is the person that sold the item.
• a request/response scheme: XACML also defines a way to query the PDP and to get responses back. A PDP can be queried either via single questions or via multiple questions in a single request e.g.:
  • Can Alice view listing 123? Yes, permit.
  • Can Alice view, edit, or delete listing 123? Permit; Deny; Deny.

With a XACML-based approach, you get to maintain your business logic and your API separate from the authorization logic. This has several benefits:

1. you can always reimplement the API and keep the same authorization model
2. you can easily expand your API without having to rewrite the authorization
3. you can change your authorization logic independently of your code
4. you can audit your authorization logic more easily
5. your authorization logic is technology-neutral. It works for REST APIs, web services, databases, and more

I recommend you check out the following resources:

1. the OASIS XACML website
2. the ALFA plugin for Eclipse - a free tool to write XACML policies.
3. The XACML developer community

There are both vendor and open-source implementations of XACML:

• Axiomatics is a vendor solution that provides both .NET and Java XACML implementations
• SunXACML is a long-standing open source Java XACML implementation

HTH, David.

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