Modern time is characterized by the accelerated development of web and mobile applications as the other web services also. People use Internet technologies in many aspects of their life such as shopping, learning, dating, work and more. Internet services have become very personalized and their use generally requires the use of a digital identity. In order to facilitate the authorization of service users, a paradigm of single sign-on has been devised. Its introduction has significantly increased the quality of the user experience, but security challenges have also emerged. This paper describes the OAuth 2.0 authorization protocol and the OIDC 1.0 authorization protocol as the main technological concepts that support the implementation of a single user login, and also analyzes the vulnerabilities of the protocols and attacks that threaten the security of the named protocols. The OIDC 1.0 protocol is specified as an upgrade to the OAuth 2.0 protocol and is primarily used for authentication purposes, while the OAuth 2.0 protocol is more used for authorization purposes. The security of protocols largely depends on the method of implementation and the tools used to implement them. Analysis of attacks can point out errors in implementation to developers but the constant development of web technologies has a great impact on security, which requires constant adjustment of authorization protocols.