Web API security

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Web API security entails authenticating programs or users who are invoking a web API.

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Along with the ease of API integrations come the difficulties of ensuring proper authentication (AuthN) and authorization (AuthZ). In a multitenant environment, security controls based on proper AuthN and AuthZ can help ensure that API access is limited to those who need (and are entitled to) it. Appropriate AuthN schemes enable producers (APIs or services) to properly identify consumers (clients or calling programs), and to evaluate their access level (AuthZ). In other words, may a consumer invoke a particular method (business logic) based on the credentials presented?

"Interface design flaws are widespread, from the world of crypto processors through sundry embedded systems right through to antivirus software and the operating system itself." [1]

Method of authentication and authorization

The most common methods for authentication and authorization include:

  1. Static strings: These are like passwords that are provided by API's to consumers.
  2. Dynamic tokens: These are time based tokens obtained by caller from an authentication service.
  3. User-delegated tokens: These are tokens such as OAuth [2] which are granted based on user authentication.
  4. Policy & attribute-based access control: policies use attributes to define how APIs can be invoked using standards such as ALFA or XACML.

The above methods provide different level of security and ease of integration. Oftentimes, the easiest method of integration also offers weakest security model.

Static strings

Basic Authentication Block Diagram Wiki basicAuth.jpg
Basic Authentication Block Diagram

In static strings method, the API caller or client embeds a string as a token in the request. This method is often referred as basic authentication. "From a security point of view, basic authentication is not very satisfactory. It means sending the user's password over the network in clear text for every single page accessed (unless a secure lower-level protocol, like SSL, is used to encrypt all transactions). Thus the user is very vulnerable to any packet sniffers on the net." [3]

Dynamic tokens

When an API is protected by a dynamic token, there is a time-based nonce inserted into the token. The token has a time to live (TTL) after which the client must acquire a new token. The API method has a time check algorithm, and if the token is expired, the request is forbidden. "An example of such token is JSON Web Token. The "exp" (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing." [4]

User-delegated token

This type of token is used in three-legged systems where an application needs to access an API on behalf of a user. Instead of revealing user id and password to the application, a user grants a token which encapsulates users permission for the application to invoke the API.

The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. [5]

Fine-Grained Authorization for APIs

Attribute-Based Access Control

In this approach, there is a Policy Enforcement Point either within the API itself, in the API framework (as an interceptor or message handler), or as an API gateway (e.g. WSO2, Kong, or similar) that intercepts the call to the API and / or the response back from the API. It converts it into an authorization request (typically in XACML) which it sends to a Policy Decision Point (PDP). The Policy Decision Point is configured with policies that implement dynamic access control that can use any number of user, resource, action, and context attributes to define which access is allowed or denied. Policies can be about:

  1. the resource (e.g. a bank account)
  2. the user (e.g. a customer)
  3. the context (e.g. time of day)
  4. a relationship (e.g. the customer to whom the account belongs).

Policies are expressed in ALFA or XACML.

Related Research Articles

Authorization or authorisation is the function of specifying access rights/privileges to resources, which is related to general information security and computer security, and to access control in particular. More formally, "to authorize" is to define an access policy. For example, human resources staff are normally authorized to access employee records and this policy is often formalized as access control rules in a computer system. During operation, the system uses the access control rules to decide whether access requests from (authenticated) consumers shall be approved (granted) or disapproved (rejected). Resources include individual files or an item's data, computer programs, computer devices and functionality provided by computer applications. Examples of consumers are computer users, computer software and other hardware on the computer.

SOCKS is an Internet protocol that exchanges network packets between a client and server through a proxy server. SOCKS5 optionally provides authentication so only authorized users may access a server. Practically, a SOCKS server proxies TCP connections to an arbitrary IP address, and provides a means for UDP packets to be forwarded.

Simple Authentication and Security Layer (SASL) is a framework for authentication and data security in Internet protocols. It decouples authentication mechanisms from application protocols, in theory allowing any authentication mechanism supported by SASL to be used in any application protocol that uses SASL. Authentication mechanisms can also support proxy authorization, a facility allowing one user to assume the identity of another. They can also provide a data security layer offering data integrity and data confidentiality services. DIGEST-MD5 provides an example of mechanisms which can provide a data-security layer. Application protocols that support SASL typically also support Transport Layer Security (TLS) to complement the services offered by SASL.

Single sign-on (SSO) is an authentication scheme that allows a user to log in with a single ID to any of several related, yet independent, software systems.

Java Authentication and Authorization Service, or JAAS, pronounced "Jazz", is the Java implementation of the standard Pluggable Authentication Module (PAM) information security framework. JAAS was introduced as an extension library to the Java Platform, Standard Edition 1.3 and was integrated in version 1.4.

The Central Authentication Service (CAS) is a single sign-on protocol for the web. Its purpose is to permit a user to access multiple applications while providing their credentials only once. It also allows web applications to authenticate users without gaining access to a user's security credentials, such as a password. The name CAS also refers to a software package that implements this protocol.

<span class="mw-page-title-main">One-time password</span> Password that can only be used once

A one-time password (OTP), also known as a one-time PIN, one-time authorization code (OTAC) or dynamic password, is a password that is valid for only one login session or transaction, on a computer system or other digital device. OTPs avoid several shortcomings that are associated with traditional (static) password-based authentication; a number of implementations also incorporate two-factor authentication by ensuring that the one-time password requires access to something a person has as well as something a person knows.

<span class="mw-page-title-main">Digest access authentication</span> Method of negotiating credentials between web server and browser

Digest access authentication is one of the agreed-upon methods a web server can use to negotiate credentials, such as username or password, with a user's web browser. This can be used to confirm the identity of a user before sending sensitive information, such as online banking transaction history. It applies a hash function to the username and password before sending them over the network. In contrast, basic access authentication uses the easily reversible Base64 encoding instead of hashing, making it non-secure unless used in conjunction with TLS.

<span class="mw-page-title-main">OpenID</span> Open and decentralized authentication protocol standard

OpenID is an open standard and decentralized authentication protocol promoted by the non-profit OpenID Foundation. It allows users to be authenticated by co-operating sites using a third-party identity provider (IDP) service, eliminating the need for webmasters to provide their own ad hoc login systems, and allowing users to log in to multiple unrelated websites without having to have a separate identity and password for each. Users create accounts by selecting an OpenID identity provider, and then use those accounts to sign on to any website that accepts OpenID authentication. Several large organizations either issue or accept OpenIDs on their websites.

Data Protection Application Programming Interface (DPAPI) is a simple cryptographic application programming interface available as a built-in component in Windows 2000 and later versions of Microsoft Windows operating systems. In theory, the Data Protection API can enable symmetric encryption of any kind of data; in practice, its primary use in the Windows operating system is to perform symmetric encryption of asymmetric private keys, using a user or system secret as a significant contribution of entropy. A detailed analysis of DPAPI inner-workings was published in 2011 by Bursztein et al.

Attribute-based access control (ABAC), also known as policy-based access control for IAM, defines an access control paradigm whereby a subject's authorization to perform a set of operations is determined by evaluating attributes associated with the subject, object, requested operations, and, in some cases, environment attributes.

<span class="mw-page-title-main">OAuth</span> Open standard for authorization

OAuth is an open standard for access delegation, commonly used as a way for internet users to grant websites or applications access to their information on other websites but without giving them the passwords. This mechanism is used by companies such as Amazon, Google, Facebook, Microsoft, and Twitter to permit users to share information about their accounts with third-party applications or websites.

Web access management (WAM) is a form of identity management that controls access to web resources, providing authentication management, policy-based authorizations, audit and reporting services (optional) and single sign-on convenience.

Distributed Access Control System (DACS) is a light-weight single sign-on and attribute-based access control system for web servers and server-based software. DACS is primarily used with Apache web servers to provide enhanced access control for web pages, CGI programs and servlets, and other web-based assets, and to federate Apache servers.

An identity provider is a system entity that creates, maintains, and manages identity information for principals and also provides authentication services to relying applications within a federation or distributed network.

SMTP Authentication, often abbreviated SMTP AUTH, is an extension of the Simple Mail Transfer Protocol (SMTP) whereby a client may log in using any authentication mechanism supported by the server. It is mainly used by submission servers, where authentication is mandatory.

User-Managed Access (UMA) is an OAuth-based access management protocol standard. Version 1.0 of the standard was approved by the Kantara Initiative on March 23, 2015.

JSON Web Token is a proposed Internet standard for creating data with optional signature and/or optional encryption whose payload holds JSON that asserts some number of claims. The tokens are signed either using a private secret or a public/private key.

IBM API Management is an API Management platform for use in the API Economy. IBM API Connect enables users to create, assemble, manage, secure and socialize web application programming interfaces (APIs).

Token Binding is a proposed standard for a Transport Layer Security (TLS) extension that aims to increase TLS security by using cryptographic certificates on both ends of the TLS connection. Current practice often depends on bearer tokens, which may be lost or stolen. Bearer tokens are also vulnerable to man-in-the-middle attacks or replay attacks. In contrast, bound tokens are established by a user agent that generates a private-public key pair per target server, providing the public key to the server, and thereafter proving possession of the corresponding private key on every TLS connection to the server.

References

  1. ↑ "API Attacks" (PDF).
  2. ↑ "OAuth 2.0 — OAuth". oauth.net. Retrieved 2015-10-10.
  3. ↑ "A Guide to Web Authentication Alternatives: Part 2". unixpapa.com. Retrieved 2015-10-10.
  4. ↑ John, Bradley; Nat, Sakimura; Michael, Jones. "JSON Web Token (JWT)". tools.ietf.org. Retrieved 2015-10-10.
  5. ↑ Hardt, Dick. "The OAuth 2.0 Authorization Framework". tools.ietf.org. Retrieved 2015-10-11.
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