How to enable SSI in Ubuntu 16.04

It appears that there is a difference in how Apache 2.2 handles <Directory> entries that align with DocumentRoot vs. how 2.4 does.

In 2.2, the following code:

DocumentRoot /var/www/myserver
<Directory />
    [...]
</Directory>

would apply any of the directives (such as Options and XBitHack) to the /var/www/myserver directory and files therein.

In 2.4, the configuration needs to change to this:

DocumentRoot /var/www/myserver
<Directory /var/www/myserver>
    [...]
</Directory>

and then apache2ctl restart, and then SSIs will work again.

I am granted access to the page and its contents are visible. This is not what I expect. However, the configuration contains Require all granted so it is expected that access to the page and its contents is granted.

Explanation

Require all

The all provider mimics the functionality that was previously provided by the 
'Allow from all' and 'Deny from all' directives. This provider can take one of two arguments
which are 'granted' or 'denied'. The following examples will grant or deny access to all
requests.

Require all granted

Require all denied

How to solve the issue

You could use mod_authn_core

Creating Authentication Provider Aliases

Extended authentication providers can be created within the configuration file and assigned
an alias name. The alias providers can then be referenced through the directives 
AuthBasicProvider or AuthDigestProvider in the same way as a base authentication provider. 
Besides the ability to create and alias an extended provider, it also allows the same 
extended authentication provider to be reference by multiple locations.

Examples

This example checks for passwords in two different text files.
Checking multiple text password files

# Check here first
<AuthnProviderAlias file file1>
    AuthUserFile "/www/conf/passwords1"
</AuthnProviderAlias>

# Then check here
<AuthnProviderAlias file file2>   
    AuthUserFile "/www/conf/passwords2"
</AuthnProviderAlias>

<Directory "/var/web/pages/secure">
    AuthBasicProvider file1 file2

    AuthType Basic
    AuthName "Protected Area"
    Require valid-user
</Directory>