Configuring Apache to rewrite urls to index.html in root directory - angularjs

Question

My AngularJS application is using html5 mode for pretty urls. The urls on my local environment work but typing full urls directly into the browser causes my test server (set up on Heroku) to respond with 404 "Not Found" errors.
Examples:
1) Typing "localhost/log_in" or "localhost" directly into the browser results the login page.
2) Typing "localhost/fkjdlfdsaf" or any other url that begins with "localhost/" directly into my browser results in the login page.
3) Typing "myapplication.herokuapp.com" (test environment) directly into the browser also results in the login page.
4) Typing "myapplication.herokuapp.com/log_in" (test environment), however, incorrectly results in a 404 "Not Found" error.
It seems like the test environment server hasn't loaded [root dir]/index.html since the file contains scripts (including a route that serves the "login" page if the url doesn't match any other routes).
Can somebody tell me what I'm missing on my test server? I prefer solutions that modify the "httpd.conf" file over using a .htaccess file.
Snippet from httpd.conf on local server:
DocumentRoot "C:/Sites/myApplication"
<Directory "C:/Sites/myApplication">
Options Indexes FollowSymLinks Includes ExecCGI
AllowOverride All
Require all granted
RewriteEngine on
# Don't rewrite files or directories
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
# Rewrite everything else to index.html to allow html5 state links
RewriteRule ^ index.html [L]
</Directory>
To configure web servers on Heroku, I created two files, procfile.txt (see this and this) as well as apache_app.conf (see this).
procfile.txt (heroku):
web: vendor/bin/heroku-php-apache2 -C apache_app.conf
apache_app.conf:
RewriteEngine on
# Don't rewrite files or directories
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
# Rewrite everything else to index.html to allow html5 state links
RewriteRule ^ index.html [L]