About Transport Layer Security
TLS, which replaced SSL, is enabled and configured with a self-signed certificate when GitHub Enterprise Server is started for the first time. As self-signed certificates are not trusted by web browsers and Git clients, these clients will report certificate warnings until you disable TLS or upload a certificate signed by a trusted authority, such as Let's Encrypt.
The GitHub Enterprise Server appliance will send HTTP Strict Transport Security headers when SSL is enabled. Disabling TLS will cause users to lose access to the appliance, because their browsers will not allow a protocol downgrade to HTTP. For more information, see "HTTP Strict Transport Security (HSTS)" on Wikipedia.
Warning: When terminating HTTPS connections on a load balancer, the requests from the load balancer to GitHub Enterprise Server also need to use HTTPS. Downgrading the connection to HTTP is not supported.
To allow users to use FIDO U2F for two-factor authentication, you must enable TLS for your instance. For more information, see "Configuring two-factor authentication."
Prerequisites
To use TLS in production, you must have a certificate in an unencrypted PEM format signed by a trusted certificate authority.
Your certificate will also need Subject Alternative Names configured for the subdomains listed in "Enabling subdomain isolation" and will need to include the full certificate chain if it has been signed by an intermediate certificate authority. For more information, see "Subject Alternative Name" on Wikipedia.
You can generate a certificate signing request (CSR) for your instance using the ghe-ssl-generate-csr command. For more information, see "Command-line utilities."
Uploading a custom TLS certificate
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From an administrative account on GitHub Enterprise Server, click in the upper-right corner of any page.
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In the left sidebar, click Management Console.
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In the left sidebar, click Privacy.
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Select TLS only (recommended).
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Under "TLS Protocol support", select the protocols you want to allow.
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Under "Certificate", click Choose File to choose a TLS certificate or certificate chain (in PEM format) to install. This file will usually have a .pem, .crt, or .cer extension.
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Under "Unencrypted key", click Choose File to choose a TLS key (in PEM format) to install. This file will usually have a .key extension.
Warning: Your TLS key must not have a passphrase. For more information, see "Removing the passphrase from your key file".
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Under the left sidebar, click Save settings.
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Wait for the configuration run to complete.
About Let's Encrypt support
Let's Encrypt is a public certificate authority that issues free, automated TLS certificates that are trusted by browsers using the ACME protocol. You can automatically obtain and renew Let's Encrypt certificates on your appliance without any required manual maintenance.
To use Let's Encrypt automation, your appliance must be configured with a hostname that is publicly accessible over HTTP. The appliance must also be allowed to make outbound HTTPS connections.
When you enable automation of TLS certificate management using Let's Encrypt, your GitHub Enterprise Server instance will contact the Let's Encrypt servers to obtain a certificate. To renew a certificate, Let's Encrypt servers must validate control of the configured domain name with inbound HTTP requests.
You can also use the ghe-ssl-acme command line utility on your GitHub Enterprise Server instance to automatically generate a Let's Encrypt certificate. For more information, see "Command-line utilities."
Configuring TLS using Let's Encrypt
To use Let's Encrypt automation, your appliance must be configured with a hostname that is publicly accessible over HTTP. The appliance must also be allowed to make outbound HTTPS connections.
- From an administrative account on GitHub Enterprise Server, click in the upper-right corner of any page.
- In the left sidebar, click Management Console.
- In the left sidebar, click Privacy.
- Select TLS only (recommended).
- Select Enable automation of TLS certificate management using Let's Encrypt.
- Under the left sidebar, click Save settings.
- Wait for the configuration run to complete.
- In the left sidebar, click Privacy.
- Click Request TLS certificate.
- Click Save configuration.