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Available since version 0.71.0
The Cosmo Router supports TLS to secure and authenticate communications for both client and subgraph connections. For subgraph connections, encryption and authentication are automatically enabled when the subgraph URL uses the https:// protocol. For client connections, you can configure TLS as follow:
config.yaml
tls:
  server:
    enabled: true
    key_file: ../your/key.pem
    cert_file: ../your/cert.pem
You must provide both files to ensure TLS.

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Use cases

  • A typical use case for TLS is to secure communications between your load balancer and router.
  • Enable HTTP/2. TLS is mandatory for HTTP/2 operation. Once enabled, requests are upgraded to HTTP/2 whenever possible.

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Cipher

By default, we inherit the defaults of Go TLS configuration. This means the following TLS protocols are supported:
  • TLS 1.3
  • TLS 1.2
  • TLS 1.1
  • TLS 1.0
We strongly advice against using TLS below 1.2 for security reasons.
In terms of cipher support, we also refer to the Go defaults: 
// AEADs w/ ECDHE
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305, TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,

// CBC w/ ECDHE
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,

// AEADs w/o ECDHE
TLS_RSA_WITH_AES_128_GCM_SHA256,
TLS_RSA_WITH_AES_256_GCM_SHA384,

// CBC w/o ECDHE
TLS_RSA_WITH_AES_128_CBC_SHA,
TLS_RSA_WITH_AES_256_CBC_SHA,

// 3DES
TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA,
TLS_RSA_WITH_3DES_EDE_CBC_SHA
If our configuration does not meet your requirements, don’t hesitate to contact us or open an issue on GitHub.

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Client Authentication or Mutual TLS (mTLS)

In a standard SSL transaction, the client verifies the server’s validity when establishing a secure connection. This involves checking the server’s certificate prior to starting the SSL transaction. However, there may be situations where you wish for the server to authenticate the client connecting to it. When client authentication is activated via client_auth.cert_file the client can send a certificate to the server that is validated by the server before a connection is established. By default it is not a requirement and the server support clients with valid and without certificates. You can set required to true to enforce that a client must be verified and authentic. If the validation does not succeed the client connection is refused.
config.yaml
tls:
  server:
    enabled: true # Required for client_auth
    key_file: ../your/key.pem
    cert_file: ../your/cert.pem
    client_auth:
      required: true
      cert_file: ../your/cert.pem
While client authentication and mTLS are closely related concepts, they are not exactly the same. mTLS is an extension of TLS (Transport Layer Security) that requires both the server and the client to authenticate each other. This ensures that both parties in a communication are who they claim to be, adding an extra layer of security. mTLS involves the exchange of certificates from both parties during the TLS handshake process. You can enable mTLS by using client_auth with required=true on the server and the correct TLS settings on the client side.

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Example in Go Clients

cert, _ := tls.LoadX509KeyPair("your/cert.pem", "your/key.pem")

caCert, _ := os.ReadFile("your/cert.pem")

caCertPool := x509.NewCertPool()
caCertPool.AppendCertsFromPEM(caCert)

client := &http.Client{
		Transport: &http.Transport{
		TLSClientConfig: &tls.Config{
			RootCAs:      caCertPool,
			Certificates: []tls.Certificate{cert},
		},
	},
}

// Make request
_, err = client.Do(req)
That’s it! The router should now be able to receive TLS connections only from clients who authenticate themselves using a certificate issued by your trusted CA.

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TLS with Subgraphs

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Router mTLS

In addition to accepting mTLS connections from clients (inbound), the router can also present client certificates when connecting to subgraphs (outbound). This is useful when your subgraphs require mTLS authentication to accept requests from the router. You can configure a global client certificate that applies to all subgraph connections, and optionally override it on a per-subgraph basis.

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Global Configuration

Apply a client certificate to all outbound subgraph connections:
config.yaml
tls:
  client:
    all:
      cert_file: /path/to/client.crt
      key_file: /path/to/client.key

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Per-Subgraph Configuration

Override the global config for specific subgraphs. Each entry fully overrides the global all config for that subgraph:
config.yaml
tls:
  client:
    all:
      cert_file: /path/to/default-client.crt
      key_file: /path/to/default-client.key
    subgraphs:
      products:
        cert_file: /path/to/products-client.crt
        key_file: /path/to/products-client.key
      inventory:
        cert_file: /path/to/inventory-client.crt
        key_file: /path/to/inventory-client.key
Per-subgraph entries live under tls.client.subgraphs and use the same field structure as tls.client.all (e.g., cert_file, key_file). A per-subgraph entry fully overrides the global all config for that subgraph.

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Custom CA Certificates

By default, the router uses your operating system’s root CA store to verify subgraph server certificates. If your subgraphs use TLS certificates signed by an internal or private CA that is not in the system’s root CA store, you can provide a custom CA certificate file using ca_file. The router will use this CA to verify the subgraph’s server certificate during the TLS handshake.
config.yaml
tls:
  client:
    all:
      ca_file: /path/to/internal-ca.crt
      insecure_skip_ca_verification: false
insecure_skip_ca_verification disables subgraph certificate validation. Only use this for development or testing environments.