Login name and password are the required information to log in to Kintone.
It is recommended to establish a password policy so that users will not choose weak passwords during password configuration.

It must be 128 characters or less.
You cannot use a login name that fits one of the following:

• The login name is already used by another user.
• The login name starts or ends with a space.
• The login name contains a special character not allowed to use for a login name.

A login name cannot contain the following special characters:

• Enter up to 64 characters.
• You can use alphanumeric characters and special characters.
• The user name is case-sensitive.
• Administrators can configure a certain level of password complexity rule (password policy).
  Users cannot configure passwords that do not satisfy the complexity requirements.

A password can contain the following special characters:

Configure it in "Security" in Kintone Users & System Administration.
For details, refer to the following page:
Specifying Password Complexity and Password Expiration