**Caddy's default TLS settings are secure. Only change these settings if you have a good reason and understand the implications.** The most common use of this directive will be to specify an ACME account email address, change the ACME CA endpoint, or to provide your own certificates.
Compatibility note: Due to its sensitive nature as a security protocol, deliberate adjustments to TLS defaults may be made in new minor or patch releases. Old or broken TLS versions, ciphers, features, etc. may be removed at any time. If your deployment is extremely sensitive to changes, you should explicitly specify those values which must remain constant, and be vigilant about upgrades. In almost every case, we recommend using the default settings.
- **protocols** <spanid="protocols"/> specifies the minimum and maximum protocol versions. Default min: `tls1.2`. Default max: `tls1.3`
- **ciphers** <spanid="ciphers"/> specifies the list of cipher suite names in descending preference order. It is recommended to not change these unless you know what you're doing. Note that cipher suites are not customizable for TLS 1.3; and not all TLS 1.2 ciphers are enabled by default. The supported names are (in no particular order here):
- **alpn** <spanid="alpn"/> is the list of values to advertise in the ALPN extension of the TLS handshake.
- **load** <spanid="load"/> specifies a list of folders from which to load PEM files that are certificate+key bundles.
- **ca** <spanid="ca"/> changes the ACME CA endpoint. This is most often used to set [Let's Encrypt's staging endpoint](https://letsencrypt.org/docs/staging-environment/) when testing, or an internal ACME server. (To change this value for the whole Caddyfile, use the `acme_ca` [global option](/docs/caddyfile/options) instead.)
- **ca_root** <spanid="ca_root"/> specifies a PEM file that contains a trusted root certificate for the ACME CA endpoint, if not in the system trust store.
- **key_type** <spanid="key_type"/> is the type of key to use when generating CSRs. Only set this if you have a specific requirement.
- **dns** <spanid="dns"/> enables the [DNS challenge](/docs/automatic-https#dns-challenge) using the specified provider plugin, which must be plugged in from one of the [caddy-dns](https://github.com/caddy-dns) repositories. Each provider plugin may have their own syntax following their name; refer to their docs for details. Maintaining support for each DNS provider is a community effort. [Learn how to enable the DNS challenge for your provider at our wiki.](https://caddy.community/t/how-to-use-dns-provider-modules-in-caddy-2/8148)
- **resolvers** <spanid="resolvers"/> customizes the DNS resolvers used when performing the DNS challenge; these take precedence over system resolvers or any default ones. If set here, the resolvers will propagate to all configured certificate issuers.
- **eab** <spanid="eab"/> configures ACME external account binding (EAB) for this site, using the key ID and MAC key provided by your CA.
- **on_demand** <spanid="on_demand"/> enables [on-demand TLS](/docs/automatic-https#on-demand-tls) for the hostnames given in the site block's address(es). **Security warning:** Doing so in production is insecure unless you also configure the [`on_demand_tls` global option](https://caddyserver.com/docs/caddyfile/options#on-demand-tls) to mitigate abuse.
- **client_auth** <spanid="client_auth"/> enables and configures TLS client authentication:
- **mode** <spanid="mode"/> is the mode for authenticating the client. Allowed values are:
Multiple `trusted_*` directives may be used to specify multiple CA or leaf certificates. Client certificates which are not listed as one of the leaf certificates or signed by any of the specified CAs will be rejected according to the **mode**.
- **issuer** <spanid="issuer"/> configures a custom certificate issuer, or a source from which to obtain certificates. Which issuer is used and the options that follow in this segment depend on the issuer modules that are available (see below for the standard issuers; plugins may add others). Some of the other subdirectives such as `ca` and `dns` are actually shortcuts for configuring the `acme` issuer (and this subdirective was added later), so specifying this directive and some of the others is confusing and thus prohibited. This subdirective can be specified multiple times to configure multiple, redundant issuers; if one fails to issue a cert, the next one will be tried.
- **get_certificate** <spanid="mode"/> configures a module that can get a certificate at handshake-time. Specifying this implicitly enables on-demand TLS as if you had specified the `on_demand` subdirective. See below for standard "certificate getter" modules.
- **dir** <spanid="dir"/> is the URL to the ACME CA's directory. Default: `https://acme-v02.api.letsencrypt.org/directory`
- **test_dir** <spanid="test_dir"/> is an optional fallback directory to use when retrying challenges; if all challenges fail, this endpoint will be used during retries; useful if a CA has a staging endpoint where you want to avoid rate limits on their production endpoint. Default: `https://acme-staging-v02.api.letsencrypt.org/directory`
- **email** <spanid="email"/> is the ACME account contact email address.
- **timeout** <spanid="timeout"/> is a [duration value](/docs/conventions#durations) that sets how long to wait before timing out an ACME operation.
- **disable_http_challenge** <spanid="disable_http_challenge"/> will disable the HTTP challenge.
- **disable_tlsalpn_challenge** <spanid="disable_tlsalpn_challenge"/> will disable the TLS-ALPN challenge.
- **alt_http_port** <spanid="alt_http_port"/> is an alternate port on which to serve the HTTP challenge; it has to happen on port 80 so you must forward packets to this alternate port.
- **alt_tlsalpn_port** <spanid="alt_tlsalpn_port"/> is an alternate port on which to serve the TLS-ALPN challenge; it has to happen on port 443 so you must forward packets to this alternate port.
- **eab** <spanid="eab"/> specifies an External Account Binding which may be required with some ACME CAs.
- **trusted_roots** <spanid="trusted_roots"/> is one or more root certificates (as PEM filenames) to trust when connecting to the ACME CA server.
- **dns** <spanid="dns"/> configures the DNS challenge.
- **propagation_timeout** <spanid="propagation_timeout"/> is a [duration value](/docs/conventions#durations) that sets how long to wait for DNS TXT records to propagate when using the DNS challenge. Default 2 minutes.
- **resolvers** <spanid="resolvers"/> customizes the DNS resolvers used when performing the DNS challenge; these take precedence over system resolvers or any default ones.
- **preferred_chains** <spanid="preferred_chains"/> specifies which certificate chains Caddy should prefer; useful if your CA provides multiple chains. Use one of the following options:
- **smallest** <spanid="smallest"/> will tell Caddy to prefer chains with the fewest amount of bytes.
- **root_common_name** <spanid="root_common_name"/> is a list of one or more common names; Caddy will choose the first chain that has a root that matches with at least one of the specified common names.
- **any_common_name** <spanid="any_common_name"/> is a list of one or more common names; Caddy will choose the first chain that has an issuer that matches with at least one of the specified common names.
The functionality of the `zerossl` issuer is the same as the `acme` issuer, except that it will use ZeroSSL's directory by default and it can automatically negotiate EAB credentials (whereas with the `acme` issuer, you have to manually provide EAB credentials and set the directory endpoint).
Certificate getter modules are distinct from issuer modules in that use of these modules imply that an external tool or service is managing the certificate, whereas an issuer module implies that Caddy is managing the certificate. Issuer modules take a Certificate Signing Request (CSR) as input, but certificate getter modules take a TLS ClientHello as input.
These getter modules come standard with the `tls` directive:
#### tailscale
Gets certificates from a locally-running Tailscale (or open source [Headscale](https://github.com/juanfont/headscale)) instance. [HTTPS must be enabled in your Tailscale account](https://tailscale.com/kb/1153/enabling-https/), and Caddy must have [permission to access the Tailscale socket](https://github.com/caddyserver/caddy/pull/4541#issuecomment-1021568348).
```caddy
... tailscale {
cache
}
```
- **cache** <spanid="cache"/> enables caching, which causes Caddy to store the certificate in its in-memory cache and reuse it until it is close to expiring or expired. If cached, Tailscale will only be accessed if the certificate needs renewal.
#### http
Gets certificates by making an HTTP(S) request. The response must have a 200 status code and the body must contain a PEM chain including the full certificate (with intermediates) as well as the private key. By default, responses will be cached within Caddy until renewal is needed unless `Cache-Control: no-cache` is set in the response header.
```caddy
... http <url>
```
- **url** <spanid="url"/> is the fully-qualified URL to which to make the request. It is strongly advised that this be a localhost endpoint for performance reasons.
Use locally-trusted certificates for all hosts on the current site block, rather than public certificates via ACME / Let's Encrypt (useful in dev environments):
Specify an email address for your ACME account (but if only one email is used for all sites, we recommend the `email` [global option](/docs/caddyfile/options) instead):
Enable TLS Client Authentication and require clients to present a valid certificate that is verified against all the provided CA's via `trusted_ca_cert_file`
