Version 8.3.7.0 Introduced on the S4810.
Version 7.6.1.0 Introduced on the S-Series.
Version 7.5.1.0 Introduced on the C-Series.
pre-Version 
6.1.1.0
Introduced on the E-Series.
Authentication and Password Commands
Use the following the commands to manage access to the system
aaa authentication enable
Configure AAA Authentication method lists for user access to EXEC privilege mode (the “Enable” access).
C-Series, E-Series, S-Series, Z-Series, S4810
Syntax
aaa authentication enable {default | method-list-name} method 
[... method2]
To return to the default setting, use the no aaa authentication enable {default 
| method-list-name} method [... method2] command.
Parameters
default Enter the keyword default followed by the authentication methods 
to use as the default sequence of methods to be used for the Enable 
log-in. The default is default enable.
method-list-name
Enter a text string (up to 16 characters long) to name the list of 
enabled authentication methods activated at log in.
method
Enter one of the following methods:
• enable - use the password defined by the enable 
password
 command in CONFIGURATION mode.
• line - use the password defined by the password 
command in LINE mode.
• none - no authentication.
• radius - use the RADIUS server(s) configured with the 
radius-server host command.
• tacacs+ - use the TACACS+ server(s) configured with the 
tacacs-server host command.
... method2
(OPTIONAL) In the event of a “no response” from the first method, 
FTOS applies the next configured method.
Defaults Use the enable password.
Command Modes CONFIGURATION
1293