---
title: HTTPS and authentication
sort_rank: 11
---

Alertmanager supports basic authentication and TLS.
This is **experimental** and might change in the future.

Currently TLS is supported for the HTTP traffic and gossip traffic.

## HTTP Traffic

To specify which web configuration file to load, use the `--web.config.file` flag.

The file is written in [YAML format](https://en.wikipedia.org/wiki/YAML),
defined by the scheme described below.
Brackets indicate that a parameter is optional. For non-list parameters the
value is set to the specified default.

The file is read upon every http request, such as any change in the
configuration and the certificates is picked up immediately.

Generic placeholders are defined as follows:

* `<boolean>`: a boolean that can take the values `true` or `false`
* `<filename>`: a valid path in the current working directory
* `<secret>`: a regular string that is a secret, such as a password
* `<string>`: a regular string

```
tls_server_config:
  # Certificate and key files for server to use to authenticate to client.
  cert_file: <filename>
  key_file: <filename>

  # Server policy for client authentication. Maps to ClientAuth Policies.
  # For more detail on clientAuth options:
  # https://golang.org/pkg/crypto/tls/#ClientAuthType
  #
  # NOTE: If you want to enable client authentication, you need to use
  # RequireAndVerifyClientCert. Other values are insecure.
  [ client_auth_type: <string> | default = "NoClientCert" ]

  # CA certificate for client certificate authentication to the server.
  [ client_ca_file: <filename> ]

  # Verify that the client certificate has a Subject Alternate Name (SAN)
  # which is an exact match to an entry in this list, else terminate the
  # connection. SAN match can be one or multiple of the following: DNS,
  # IP, e-mail, or URI address from https://pkg.go.dev/crypto/x509#Certificate.
  [ client_allowed_sans:
    [ - <string> ] ]

  # Minimum TLS version that is acceptable.
  [ min_version: <string> | default = "TLS12" ]

  # Maximum TLS version that is acceptable.
  [ max_version: <string> | default = "TLS13" ]

  # List of supported cipher suites for TLS versions up to TLS 1.2. If empty,
  # Go default cipher suites are used. Available cipher suites are documented
  # in the go documentation:
  # https://golang.org/pkg/crypto/tls/#pkg-constants
  #
  # Note that only the cipher returned by the following function are supported:
  # https://pkg.go.dev/crypto/tls#CipherSuites
  [ cipher_suites:
    [ - <string> ] ]

  # prefer_server_cipher_suites controls whether the server selects the
  # client's most preferred ciphersuite, or the server's most preferred
  # ciphersuite. If true then the server's preference, as expressed in
  # the order of elements in cipher_suites, is used.
  [ prefer_server_cipher_suites: <bool> | default = true ]

  # Elliptic curves that will be used in an ECDHE handshake, in preference
  # order. Available curves are documented in the go documentation:
  # https://golang.org/pkg/crypto/tls/#CurveID
  [ curve_preferences:
    [ - <string> ] ]

http_server_config:
  # Enable HTTP/2 support. Note that HTTP/2 is only supported with TLS.
  # This can not be changed on the fly.
  [ http2: <boolean> | default = true ]
  # List of headers that can be added to HTTP responses.
  [ headers:
    # Set the Content-Security-Policy header to HTTP responses.
    # Unset if blank.
    [ Content-Security-Policy: <string> ]
    # Set the X-Frame-Options header to HTTP responses.
    # Unset if blank. Accepted values are deny and sameorigin.
    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
    [ X-Frame-Options: <string> ]
    # Set the X-Content-Type-Options header to HTTP responses.
    # Unset if blank. Accepted value is nosniff.
    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
    [ X-Content-Type-Options: <string> ]
    # Set the X-XSS-Protection header to all responses.
    # Unset if blank.
    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection
    [ X-XSS-Protection: <string> ]
    # Set the Strict-Transport-Security header to HTTP responses.
    # Unset if blank.
    # Please make sure that you use this with care as this header might force
    # browsers to load Prometheus and the other applications hosted on the same
    # domain and subdomains over HTTPS.
    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Strict-Transport-Security
    [ Strict-Transport-Security: <string> ] ]

# Usernames and hashed passwords that have full access to the web
# server via basic authentication. If empty, no basic authentication is
# required. Passwords are hashed with bcrypt.
basic_auth_users:
  [ <string>: <secret> ... ]
```

## Gossip Traffic

To specify whether to use mutual TLS for gossip, use the `--cluster.tls-config` flag.

The server and client sides of the gossip are configurable.

```
tls_server_config:
  # Certificate and key files for server to use to authenticate to client.
  cert_file: <filename>
  key_file: <filename>

  # Server policy for client authentication. Maps to ClientAuth Policies.
  # For more detail on clientAuth options:
  # https://golang.org/pkg/crypto/tls/#ClientAuthType
  [ client_auth_type: <string> | default = "NoClientCert" ]

  # CA certificate for client certificate authentication to the server.
  [ client_ca_file: <filename> ]

  # Minimum TLS version that is acceptable.
  [ min_version: <string> | default = "TLS12" ]

  # Maximum TLS version that is acceptable.
  [ max_version: <string> | default = "TLS13" ]

  # List of supported cipher suites for TLS versions up to TLS 1.2. If empty,
  # Go default cipher suites are used. Available cipher suites are documented
  # in the go documentation:
  # https://golang.org/pkg/crypto/tls/#pkg-constants
  [ cipher_suites:
    [ - <string> ] ]

  # prefer_server_cipher_suites controls whether the server selects the
  # client's most preferred ciphersuite, or the server's most preferred
  # ciphersuite. If true then the server's preference, as expressed in
  # the order of elements in cipher_suites, is used.
  [ prefer_server_cipher_suites: <bool> | default = true ]

  # Elliptic curves that will be used in an ECDHE handshake, in preference
  # order. Available curves are documented in the go documentation:
  # https://golang.org/pkg/crypto/tls/#CurveID
  [ curve_preferences:
    [ - <string> ] ]

tls_client_config:
  # Path to the CA certificate with which to validate the server certificate.
  [ ca_file: <filepath> ]

  # Certificate and key files for client cert authentication to the server.
  [ cert_file: <filepath> ]
  [ key_file: <filepath> ]

  # Server name extension to indicate the name of the server.
  # http://tools.ietf.org/html/rfc4366#section-3.1
  [ server_name: <string> ]

  # Disable validation of the server certificate.
  [ insecure_skip_verify: <boolean> | default = false]
```
