## 1 Introduction  
Cloud authentication verifies user identities across a cloud platform to determine whether the user is trusted to access cloud applications, data, services, and resources by ensuring access rights and privileges. The lack of strong and appropriate cloud authentication techniques leads to the occurrence of some cloud security threats and attacks. Some of the most common cloud threats are information disclosure, Denial-of-Service (DoS), spoofing identity, data tampering, repudiation, account hijacking, and the elevation of privilege [1,2]. Cloud-based authentication attacks include DoS attacks, Man-in-the-Middle (MITM) attacks, Replay attacks, Cloud Malware Injection attacks, Password Discoveryattacks, Reflection attacks, Customer Fraud attacks, Insider attacks, and Known Session-Specific Temporary Information (KSSTI) attacks [3, 4]. Indeed, various possible authentication techniques are the first barrier of defense against various attacks that prevent unauthorized access to applications, data, services, and resources. Some such techniques include password-based authentication, Single Sign-On (SSO) [5], token authentication, graphical password authentication, biometric authentication, third-party authentication [6], certificate-based authentication [7], digital device authentication, two-factor authentication, and multi-factor authentication (MFA) [8, 9, 10]. More recently, organizations have implemented and used MFA in cloud applications to increase security and productivity, reduce the risk of compromised passwords, improve regulatory compliance, and enable enterprise mobility [11]. MFA in cloud computing primarily relies on electronic or digital authentication techniques in which a cloud user is allowed to access either data, application, service, or resource only after two or more factors have been successfully submitted [12]. In the literature, these factors are categorized into knowledge factors, possession factors, inheritance factors, location factors, time factors, behavior factors, processing factors, and personal knowledge factors [13]. The knowledge factors are the already known things such as the personal identification number (PIN), password, security question, one-time code, and passphrase. The possession factors, referred to also as token-based factors, are the owned things such as identity cards, SIM cards, memory cards, smartcards, Fast Identity Online (FIDO) security keys, one-time password tokens, and smartphones with an OTP app. The inheritance factors are the integral elements of a person in the form of biometric data such as iris scans, fingerprint scans, and voice recognition. The location factors are those factors that determine where a person is supposed to be located, such as IP addresses and MAC addresses. Time factors are those factors that are used to detect the presence of a person at a scheduled time of day or within a scheduled time interval. The behavior factors are the actions by which a person can be identified and authorized, such as keystroke rhythm, gait, and mouse usage [11, 14]. Processing factors are factors that depend on the level of human perception to perform or memorize a mathematical or logical operation. Personal knowledge factors are implemented based on a person's social relationships by asking someone how much they know the person being asked for validation. When using MFA, in case one factor is compromised by an unauthorized user, the chances of another factor being compromised are low. Therefore, MFA represents a higher degree of assurance about a user's identity. Further information regarding the convenience and importance of MFA for ensuring secure access to the cloud can be found in [15]. In this paper, we proposed a multi-factor multi-layer authentication framework with a variety of user authentication choices to achieve the following contributions. 1. Providing a concise survey that clarifies the existence of various cloud MFA authentication techniques using multiple numbers of factors. 2.