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README.md

Let's Encrypt Site Extension

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This Azure Web App Site Extension enables easy installation and configuration of Let's Encrypt issued SSL certificates for you custom domain names.

The site extension requires that you have configured a DNS entry for your custom domain to point to Azure Web App.

November 2019 - Microsoft finally acknowledge that maybe it is in due time that they add first level support for free SSL certificates, see this announcement about App Service Managed Certificates, be aware that it is in preview and currently doesn't support the apex/naked domain.

How to install

https://github.com/sjkp/letsencrypt-siteextension/wiki/How-to-install

Known Issues

  • This site-extension is NOT supported by Microsoft it is my own work based on https://github.com/fszlin/certes - this means don't expect 24x7 support, I use it for several of my own smaller sites, but if you are running sites that are important you should consider spending the few $ on a certificate and go with a Microsoft supported way of enabling SSL, so you have someone to blame :)
  • Note that Let's Encrypt works by providing automated certificates of a short (currently three month) duration. This extension is BETA SOFTWARE. You will need to keep this extension updated or risk losing SSL access when your certificate expires.
  • There are presently no email notifications for certificate renewal problems, but Lets Encrypt will email you weeks in advance of certificate expiration, when the extension is running properly the certificate should have been renewed before Let's Encrypt send the reminder email.
  • Due to rate limiting of Let's Encrypt servers, you can only request five certificates per domain name per week. Configuration errors or errors in this site extension may render you unable to retrieve a new certificate for seven days. If up-time is critical, have a plan for deploying a SSL certificate from another source in place.
  • No support for multi-region web apps, so if you use traffic manager or some other load balancer to route traffic between web apps in different regions please dont use this extension.
  • If you publish your project from Visual Studio with the "Delete Existing files" option, you will remove the web jobs the site extension uses to renew the certificate once they expire every 3 months (you can renew them manually or install the site extension again after publish).
  • The site-extension can now work with Azure App Service Local Cache, however you must do a little manual work, see https://github.com/sjkp/letsencrypt-siteextension/wiki/Azure-Function,-Multi-Region,-Local-Cache-support
  • If you use the "Run From Zip" deployment method, please take a look at this: https://github.com/sjkp/letsencrypt-siteextension/issues/239#issuecomment-440785470
  • Wildcard domains are not supported, (and will not be supposed in the site-extension), if you are interested in wildcard support check https://github.com/sjkp/letsencrypt-azure
  • If you have picked .net core as the runtime on a brand new web site, the extension will not work properly https://github.com/sjkp/letsencrypt-siteextension/issues/349

How to troubleshoot

https://github.com/sjkp/letsencrypt-siteextension/wiki/Troubleshoot

This is Beta Software

Please take note that this Site-Extension is beta-software, so use at your own risk.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYLEFT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Semi-Automated Installation

With the semi-automated installation you manually add the site extension to your web app. Open the extension and manually click through the 3 step dialog.

Once this process is complete your custom domain for the site is setup with a Let's Encrypt issued SSL certificate.

Fully-Automated Installation

To use the Fully Automated Installation the following Web App settings must be added.

Key Value
letsencrypt:Tenant The tenant name e.g. myazuretenant.onmicrosoft.com
letsencrypt:SubscriptionId The subscription id
letsencrypt:ClientId The value of the clientid of the service principal
letsencrypt:ClientSecret The secret for the service principal
letsencrypt:ResourceGroupName The name of the resource group this web app belongs to
letsencrypt:ServicePlanResourceGroupName The name of the resource group with the app service plan that hosts the web app, if the app service plan is in the same plan as the web app, then this property is optional.
letsencrypt:AcmeBaseUri The url to Let's Encrypt servers e.g. https://acme-v02.api.letsencrypt.org/directory or https://acme-staging-v02.api.letsencrypt.org/directory (defaults to this)
letsencrypt:Email The Email used for registering with Let's Encrypt
letsencrypt:Hostnames Comma separated list of custom hostnames (externally hosted setup with CNames), that should automatically be configured for the site.
letsencrypt:WebRootPath Use this setting, if you are not serving the website from site\wwwroot, then you can specify the other folder that serves your website here - should be in the format d:\home\site\wwwroot\public or where ever your files are located on the web server.
letsencrypt:DisableWebConfigUpdate true / false, defaults to false, set this to true if you don't want the site extension to write the default webconfig to wwwroot.well-known\acme-challenge
letsencrypt:SiteSlot Use this setting if you want to use the extension to setup SSL certificate for deployment slots, the value should be the name of the slot (and the extension should be installed in that slots kudu portal)
letsencrypt:UseIPBasedSSL Set to true if you want to use IP Based SSL (required by some older clients). Defaults to false, which results in SNI.
letsencrypt:RenewXNumberOfDaysBeforeExpiration Set to an integer defining the number of days before expiration the certificates should be renewed. Defaults to 22 days before expiration, as letencrypt sends reminder emails 20 days before
letsencrypt:AuthorizationChallengeBlobStorageAccount (Optional) Set this setting to the connection string of a storage account, if you want to persist the http challenge file to an external azure blob storage, and serve it yourself when let's encrypt request it from the http://yourdomain/.well-known/acme-challenge/{filename} path. (Can be used when local file system cache is enabled or the web app is deployed to multiple region behind traffic manager etc.)
letsencrypt:AuthorizationChallengeBlobStorageContainer Used in conjuction with letsencrypt:AuthorizationChallengeBlobStorageAccount if you want to specify the name of the container that is used, if not specified then letsencrypt-siteextension is used

As it can be seen from the list of App Settings a service principal is needed. The service principal must be assigned permissions to the web app, that is required as the extension use it for installing and updating the certificate. (If two resource groups are used, the app service principal must have access to both).

Besides the App Settings, the two Azure Web Job required connection strings AzureWebJobsStorage and AzureWebJobsDashboard must also exists, as the extension relies on an internal Web Job to renew the certificates once they expire.

To see an example of an ARM template installation look at azuredeploy.json

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