The actions or input data of your users, during the sign up or the log in processes, might trigger errors. This article lists the most common errors that you might get, if you use any of the Auth0 libraries for authentication.

In the case of a failed signup, the most common errors are:

Error	Description
user_exists	The user you are attempting to sign up has already signed up
username_exists	The username you are attempting to sign up with is already in use
unauthorized	If you cannot sign up for this application. May have to do with the violation of a specific rule
invalid_password	If the password used doesn't comply with the password policy for the connection
password_dictionary_error	The chosen password is too common
password_no_user_info_error	The chosen password is based on user information
password_strength_error	The chosen password is too weak

In the case of a failed login, the most common errors are:

Error	Description
unauthorized	The user you are attempting to sign in with is blocked
too_many_attempts	The account is blocked due to too many attempts to sign in
password_leaked	If the password has been leaked and a different one needs to be used
mfa_required	The user must provide the multifactor authentication code to authenticate
mfa_registration_required	The administrator has required multifactor authentication, but the user has not enrolled
mfa_invalid_code	The multifactor authentication code provided by the user is invalid/expired
PasswordStrengthError	The password provided does not match the connection's strength requirements
PasswordHistoryError	The password provided for sign up/update has already been used (reported when password history feature is enabled)
invalid_user_password	The username and/or password used for authentication are invalid
access_denied	When using web-based authentication, the resource server denies access per OAuth2 specifications