OAuth2 is an authorization delegation protocol that allows one party’s accessing of an end user’s resources stored with another party without sharing any credentials. OAuth2 is often compared with SAML and OpenID Connect as their purposes and uses overlap, however these comparisons often refer to OAuth2 as OAuth. This has resulted in some confusion regarding OAuth2 and OAuth1.

OAuth1 was published in 2010, and OAuth2 is a complete rewrite of OAuth1 released in 2012. The following section will go over the most significant needs that led to this rewrite, along with the change associated to address them.

Support for non-browser based applications

One of the commonly agreed-upon disadvantages of OAuth1 was the lack of support it offers to non-browser based application clients. OAuth2 has different authorization work flows to address authorization initiated by native application clients. This was one of the main advantages OAuth2 has over OAuth1. However, abuse of the flows in favour of convenience and ease can lead to insecure implementations of OAuth2. When using OAuth2 for mobile, desktop, or single page applications, it is recommended to refer to the IETF paper going over best OAuth2 practices for mobile apps: https://tools.ietf.org/html/rfc8252.

Ease of implementation

OAuth1 was often criticized for the barrier it poses to writing a client as each exchange between client, server, and resource server requires a validation of a shared secret. This secret is used to sign the arguments for the authorization request by the client, subsequently the server signs the arguments with the client’s key to verify the legitimacy of the client. The arguments need to be passed in the exact order and is often finicky to write. Moreover, dealing with cryptographic signing of the requests in addition to this can be a pain.

OAuth2 has delegated this part of the security to transfer over HTTPS. This means while OAuth1 is protocol-independent, OAuth2 requests must be sent over SSL. Since TLS already provides transport-level message privacy and integrity, some question the merit of arguably redundant client-side signing and argument sorting. Others have brought up concerns with completely delegating security to HTTPS, and mention reasons such as yet-undiscovered zero-day TLS vulnerabilities potentially compromising entire systems.

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