No,you don't need to implement all code to handle the authentication ,you can inherit from existing class that alfresco provided.
The easiest way to do it like this:
For example if you use the default authentication chain,you can just customize your own class and inherit org.alfresco.repo.security.authentication.AuthenticationComponentImpl,the only methd you have to override is following
@Override
protected void authenticateImpl(final String userNameIn, final char[] password) throws AuthenticationException{
super.authenticateImpl(userNameIn, password);
//add your code here
}
create a spring configuration name file like ***-context.xml with content like following and place it into alfresco/extension/subsystems//Authentication/alfrescoNtlm
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE beans PUBLIC '-//SPRING//DTD BEAN//EN' 'http://www.springframework.org/dtd/spring-beans.dtd'>
<beans>
<bean id="authenticationComponent" class="******.YourAuthenticationComponentImpl"
parent="authenticationComponentBase">
<property name="authenticationDao">
<ref bean="authenticationDao" />
</property>
<property name="authenticationManager">
<ref bean="authenticationManager" />
</property>
<property name="compositePasswordEncoder">
<ref bean="compositePasswordEncoder" />
</property>
<property name="allowGuestLogin">
<value>${alfresco.authentication.allowGuestLogin}</value>
</property>
<property name="nodeService">
<ref bean="nodeService" />
</property>
<property name="personService">
<ref bean="personService" />
</property>
<property name="transactionService">
<ref bean="transactionService" />
</property>
<!-- -->
<!-- A list of default users with admin rights. -->
<!-- -->
<!-- If the security framework is case sensitive these values should -->
<!-- be case sensitive user names. If the security framework is not -->
<!-- case sensitive these values should be the lower-case user names. -->
<!-- -->
<!-- By default this includes: -->
<!-- admin (the user name of default alfresco admin user) -->
<!-- administrator (the windows default admin user) -->
<!-- -->
<!-- This assumes that user names are not case sensitive. -->
<!-- -->
<property name="defaultAdministratorUserNames">
<set>
<value>${alfresco_user_store.adminusername}</value>
<value>administrator</value>
</set>
</property>
<!-- -->
<!-- A list of default users acting as guests. -->
<!-- -->
<!-- By default this includes: -->
<!-- guest (the user name of default alfresco guest user) -->
<!-- -->
<!-- This assumes that user names are not case sensitive. -->
<!-- -->
<property name="defaultGuestUserNames">
<set>
<value>${alfresco_user_store.guestusername}</value>
</set>
</property>
</bean>
</beans>
And same as Axel Faust ,I also recommend using audit component
