Azure web app redirect http to https

Go to Azure portal and open the overview page of the (Web) App Service you wanna set to HTTPS only. In the sidebar, under the Settings section, there is an option for TLS/SSL Settings.

On clicking it, you will get an option on the screen to set your app's protocol to HTTPS only. There isn't any need to manually add separate ruleset for this.

This works on every tier of App Service Plan including the 'F'-Series (free subscription).

Note that, if you are adding any custom domain you also need to add corresponding SSL bindings, you can easily get them using LetsEncrypt or alike. If any of the custom hostnames for your app are missing SSL bindings, then:

When HTTPS Only is enabled clients accessing your app on those custom hostnames will see security warnings.

_{PS: I just saw that this question was asked about 3 years ago and that time maybe there was no direct option to do this. But even so, I'm posting my answer because on Google (as on February 2020) this question still ranks first among others regd. automatic HTTPS redirection in Azure.}

As of November 2017, this is now a simple switch in the Azure Portal: "HTTPS Only", under Custom domains.

https://blogs.msdn.microsoft.com/benjaminperkins/2017/11/30/how-to-make-an-azure-app-service-https-only/

It's also very easy in ARM: “httpsOnly”: true

There is also a free and open source extension for this.

1. Go to your Web App settings sidebar, search for the "Extensions" tab and click on "Add".

2. Scroll down and find the extension Redirect HTTP to HTTPS by gregjhogan.

3. Accept the terms.

4. Restart the Web App for the actions to take effect immediately.

5. Done !

For further details on the implementation of this extension, check the source code on GitHub. The most important source file is the applicationhost.xdt.

Quote from GitHub (02-08-2017) (credits go to gregjhogan):

applicationhost.xdt

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
    <location path="%XDT_SITENAME%" xdt:Transform="InsertIfMissing" xdt:Locator="Match(path)">
        <system.webServer xdt:Transform="InsertIfMissing">
            <rewrite xdt:Transform="InsertIfMissing">
                <rules xdt:Transform="InsertIfMissing" lockElements="clear">
                    <rule name="redirect HTTP to HTTPS" enabled="true" stopProcessing="true" lockItem="true">
                        <match url="(.*)" />
                        <conditions>
                            <add input="{HTTPS}" pattern="off" ignoreCase="true" />
                            <add input="{WARMUP_REQUEST}" pattern="1" negate="true" />
                        </conditions>
                        <action type="Redirect" url="https://{HTTP_HOST}/{R:1}" appendQueryString="true" redirectType="Permanent" />
                    </rule>
                </rules>
            </rewrite>
        </system.webServer>
    </location>
</configuration>

R:1 is a back-reference to the rule pattern. You append that to the url here:

url="https://{HTTP_HOST}/{R:1}" 

changing that into

url="https://{HTTP_HOST}" 

should result in a redirect to the https root.