Set up mutual TLS with a private CA

This page provides instructions for creating a private certificate authority (CA) by using the Certificate Authority Service and uploading your certificates to a Certificate Manager TrustConfig resource.

You also create the network security resources required for configuring mutual TLS for Application Load Balancers.

Before you begin

• Review the Mutual TLS overview.

• Install the Google Cloud CLI. For a complete overview of the tool, see the gcloud CLI overview. You can find commands related to load balancing in the API and gcloud CLI reference.

  If you haven't run the gcloud CLI previously, first run gcloud init to authenticate.

• Make sure that you know how to create CA pools.

• If you are using global external Application Load Balancer or classic Application Load Balancer, make sure you have set up a load balancer with any of the following supported backends:

  • VM instance group backends
  • Cloud Storage buckets (Supported only if there is at least one backend service also attached to the load balancer, in addition to the backend bucket)
  • Cloud Run, App Engine, or Cloud Run functions
  • Hybrid connectivity

• If you are using regional external Application Load Balancer, cross-region internal Application Load Balancer, or regional internal Application Load Balancer, make sure you have set up a load balancer with any of the following supported backends:

  • VM instance group backends
  • Cloud Run
  • Hybrid connectivity

Permissions

To get the permissions that you need to complete this guide, ask your administrator to grant you the following IAM roles on the project:

• To create load balancer resources such as TargetHTTPProxy: Compute Load Balancer Admin (roles/compute.loadBalancerAdmin)
• To use Certificate Manager resources: Certificate Manager Owner (roles/certificatemanager.owner)
• To create security and networking components: Compute Network Admin (roles/compute.networkAdmin) and Compute Security Admin (roles/compute.securityAdmin)
• To create a project (optional): Project Creator (roles/resourcemanager.projectCreator)

For more information about granting roles, see Manage access to projects, folders, and organizations.

You might also be able to get the required permissions through custom roles or other predefined roles.

Note: IAM basic roles might also contain permissions to complete this guide. You shouldn't grant basic roles in a production environment, but you can grant them in a development or test environment.

Create a root CA in the CA pool

To create a root CA in the private CA pool, complete the following steps:

1. To create a CA pool, use the gcloud privateca pools create command:

   gcloud privateca pools create CA_POOL \
      --location=us-central1
   

   Replace CA_POOL with the ID or name of the parent CA pool.

2. To create a root CA in the CA pool, use the gcloud privateca roots create command:

   gcloud privateca roots create CA_ROOT \
      --pool=CA_POOL \
      --subject="CN=my-ca, O=Test LLC" \
      --location=us-central1
   

   Replace the following:

   • CA_ROOT: the ID or name of the root CA.
   • CA_POOL: the ID or name of the parent CA pool.

3. To describe the new CA and create the root.cert file, use the gcloud privateca roots describe command:

   gcloud privateca roots describe CA_ROOT \
      --pool=CA_POOL \
      --location=us-central1 \
      --format='value(pemCaCertificates)' > root.cert
   

   Replace the following:

   • CA_ROOT: the ID or name of the private CA.
   • CA_POOL: the ID or name of the parent CA pool.

4. Format the certificate into a single line and store it in an environmental variable so that it can be referenced by the trust config YAML file.

   export ROOT=$(cat root.cert | sed 's/^[ ]*//g' | tr '\n' $ | sed 's/\$/\\n/g')
   

   For more information, see the following:

   • Create a CA pool
   • Create a root CA

Create a trust config resource

A trust config is a resource that represents your Public Key Infrastructure (PKI) configuration in Certificate Manager.

To create a trust config resource, complete the following steps:

Console

1. In the Google Cloud console, go to the Certificate Manager page.

   Go to Certificate Manager

2. On the Trust Configs tab, click Add Trust Config.

3. Enter a name for the configuration.

4. For Location, select Global or Regional.

   The location denotes where the trust config resource is stored. For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, create a global trust config resource. For regional external Application Load Balancers and regional internal Application Load Balancers, create a regional trust config resource.

   If you selected Regional, select the region.

5. In the Trust store section, click Add trust anchor and upload the PEM-encoded certificate file, or copy the contents of the certificate.

6. Click Add.

7. Click Create.

Verify that the new trust config resource appears in the list of configurations.

gcloud

1. Create a trust config YAML file (trust_config.yaml) that specifies the trust config parameters. In this example, the trust config resource is a trust store with a single trust anchor that represents a root certificate. This root certificate is generated using the private CA.

   cat << EOF > trust_config.yaml
   name: TRUST_CONFIG_NAME
   trustStores:
   - trustAnchors:
       - pemCertificate: "${ROOT?}"
   EOF
   

2. To import the trust config YAML file, use the gcloud certificate-manager trust-configs import command:

   global

   For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, specify global as the location where the trust config resource is stored.

   gcloud certificate-manager trust-configs import TRUST_CONFIG_NAME  \
       --source=trust_config.yaml \
       --location=global
   

   Replace the following:

   • TRUST_CONFIG_NAME: the name of the trust config resource.

   regional

   For regional external Application Load Balancers and regional internal Application Load Balancers, specify the region where the trust config resource is stored.

   gcloud certificate-manager trust-configs import TRUST_CONFIG_NAME  \
       --source=trust_config.yaml \
       --location=LOCATION
   

   Replace the following:

   • TRUST_CONFIG_NAME: the name of the trust config resource.
   • LOCATION: the region where the trust config resource is stored. The default location is global.

Create a Client Authentication resource

A Client Authentication (also called ServerTLSPolicy) resource lets you specify the server-side TLS mode and the trust config resource to use when validating client certificates. When the client presents an invalid certificate or no certificate to the load balancer, the clientValidationMode specifies how the client connection is handled. For more information, see mTLS client validation modes.

• When the clientValidationMode is set to ALLOW_INVALID_OR_MISSING_CLIENT_CERT, all requests are passed to the backend even if the validation fails or the client certificate is missing.
• When the clientValidationMode is set to REJECT_INVALID, only requests that supply a client certificate that can be validated against a TrustConfig resource are passed to the backend.

To create a Client Authentication (ServerTlsPolicy) resource, complete the following steps:

Console

1. In the Google Cloud console, go to the Client Authentication page.

   Go to Client Authentication

2. Click Create Client Authentication.

3. Enter a name for the Client Authentication resource.

4. For Location, select Global or Regional.

   For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, set the location to global. For regional external Application Load Balancers and regional internal Application Load Balancers, set the location to the region where the load balancer is configured.

5. For Client Authentication mode, select Load balancing.

6. Select a client validation mode.

7. Select the trust config resource that you created earlier.

8. Click Create.

Verify that the Client Authentication (ServerTlsPolicy) is displayed.

gcloud

1. Based on how you want to handle the connection, select one of the following options to define the Client Authentication (ServerTlsPolicy) resource in YAML format.

   • Option 1: clientValidationMode is set to ALLOW_INVALID_OR_MISSING_CLIENT_CERT.

     global

     For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, create a YAML file that declaratively specifies the client validation mode and a global trust config resource:

     cat << EOF > server_tls_policy.yaml
     name: SERVER_TLS_POLICY_NAME
     mtlsPolicy:
         clientValidationMode: ALLOW_INVALID_OR_MISSING_CLIENT_CERT
         clientValidationTrustConfig: projects/PROJECT_ID/locations/global/trustConfigs/TRUST_CONFIG_NAME
     EOF
     

     regional

     For regional external Application Load Balancers and regional internal Application Load Balancers, create a YAML file that declaratively specifies the client validation mode and a regional trust config resource:

     cat << EOF > server_tls_policy.yaml
     name: SERVER_TLS_POLICY_NAME
     mtlsPolicy:
         clientValidationMode: ALLOW_INVALID_OR_MISSING_CLIENT_CERT
         clientValidationTrustConfig: projects/PROJECT_ID/locations/REGION/trustConfigs/TRUST_CONFIG_NAME
     EOF
     

   • Option 2: clientValidationMode is set to REJECT_INVALID.

     global

     For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, create a YAML file that declaratively specifies the client validation mode and a global trust config resource:

     cat << EOF > server_tls_policy.yaml
     name: SERVER_TLS_POLICY_NAME
     mtlsPolicy:
         clientValidationMode: REJECT_INVALID
         clientValidationTrustConfig: projects/PROJECT_ID/locations/global/trustConfigs/TRUST_CONFIG_NAME
     EOF
     

     regional

     For regional external Application Load Balancers and regional internal Application Load Balancers, create a YAML file that declaratively specifies the client validation mode and a regional trust config resource:

     cat << EOF > server_tls_policy.yaml
     name: SERVER_TLS_POLICY_NAME
     mtlsPolicy:
           clientValidationMode: REJECT_INVALID
           clientValidationTrustConfig: projects/PROJECT_ID/locations/REGION/trustConfigs/TRUST_CONFIG_NAME
     EOF
     

     Replace the following:

     SERVER_TLS_POLICY_NAME: the name of the Client Authentication (ServerTlsPolicy) resource.

     PROJECT_ID: the ID of your Google Cloud project.

     LOCATION: for global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, use global. For regional external Application Load Balancer or regional internal Application Load Balancer, use the region where you configured the load balancer.

     TRUST_CONFIG_NAME: the name of the trust config resource that you created earlier.

2. To import the Client Authentication ServerTlsPolicy resource, use the gcloud network-security server-tls-policies import command:

   global

   For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, set the --location flag to global.

   gcloud network-security server-tls-policies import SERVER_TLS_POLICY_NAME \
     --source=server_tls_policy.yaml \
     --location=global
   

   Replace the following:

   SERVER_TLS_POLICY_NAME: the name of the Client Authentication (ServerTlsPolicy) resource.

   regional

   For regional external Application Load Balancers and regional internal Application Load Balancers, set the --location flag to the region where the load balancer is configured.

   gcloud network-security server-tls-policies import SERVER_TLS_POLICY_NAME \
     --source=server_tls_policy.yaml \
     --location=LOCATION
   

   Replace the following:

   SERVER_TLS_POLICY_NAME: the name of the Client Authentication (ServerTlsPolicy) resource.

3. Optional: To list all the Client Authentication (ServerTlsPolicies) resources, use the gcloud network-security server-tls-policies list command:

   gcloud network-security server-tls-policies list \
     --location=LOCATION
   

   Replace the following:

   LOCATION: For global external Application Load Balancers, classic Application Load Balancers, and cross-region internal Application Load Balancers, use global. For regional external Application Load Balancer or regional internal Application Load Balancer, use the region where you configured the load balancer.

Note: To modify the Client Authentication (ServerTlsPolicy) resource, you must first delete the existing Client Authentication resource and then create a new Client Authentication resource. You can then attach the Client Authentication resource to the target HTTPS proxy of the load balancer.

Attach the Client Authentication resource to the load balancer

For mutual TLS authentication to work, after you set up your load balancer, you need to attach the Client Authentication (ServerTLSPolicy) resource to the target HTTPS proxy resource of the load balancer.

Console

1. In the Google Cloud console, go to the Load balancing page.

   Go to Load balancing

2. From the list of load balancers, select the load balancer to which you need to attach the Client Authentication (ServerTLSPolicy) resource to.

3. Click Edit.

4. In the Frontend configuration section for an HTTPS frontend, expand the Show Advanced features section.

5. From the Client Authentication list, select the Client Authentication resource.

6. Click Done.

7. Click Update.

gcloud

1. To list all the target HTTPS proxy resources in your project, use the gcloud compute target-https-proxies list command:

   gcloud compute target-https-proxies list
   

   Note the name of the target HTTPS proxy to attach the ServerTLSPolicy resource to. This name is referred to as TARGET_HTTPS_PROXY_NAME in the following steps.

2. To export a target HTTPS proxy's configuration to a file, use the gcloud compute target-https-proxies export command.

   global

     gcloud compute target-https-proxies export TARGET_HTTPS_PROXY_NAME \
         --destination=TARGET_PROXY_FILENAME \
         --global
     

   Replace the following:

   • TARGET_HTTPS_PROXY_NAME: the name of the target proxy.
   • TARGET_PROXY_FILENAME: the name of the target proxy's configuration file in YAML format. For example, mtls_target_proxy.yaml.

   regional

   gcloud compute target-https-proxies export TARGET_HTTPS_PROXY_NAME \
       --destination=TARGET_PROXY_FILENAME \
       --region=REGION
   

   Replace the following:

   • TARGET_HTTPS_PROXY_NAME: the name of the target proxy.
   • TARGET_PROXY_FILENAME: the name of the target proxy's configuration file in YAML format. For example, mtls_target_proxy.yaml
   • REGION: the region where you configured the load balancer.

3. To list all the Client Authentication (ServerTlsPolicy) resources, use the gcloud network-security server-tls-policies list command:

   gcloud network-security server-tls-policies list \
       --location=LOCATION
   

   Replace the following:

   LOCATION: for cross-region internal Application Load Balancer, global external Application Load Balancer, or classic Application Load Balancer, use global. For regional external Application Load Balancer or regional internal Application Load Balancer, use the region where you configured the load balancer.

   Note the name of the Client Authentication (ServerTLSPolicy) resource to configure mTLS. This name is referred to as SERVER_TLS_POLICY_NAME in the next step.

4. Append the Client Authentication (ServerTlsPolicy) to the target HTTPS proxy.

   echo "serverTlsPolicy: //networksecurity.googleapis.com/projects/PROJECT_ID/locations/LOCATION/serverTlsPolicies/SERVER_TLS_POLICY_NAME" >> TARGET_PROXY_FILENAME
   

   Replace the following:

   • PROJECT_ID: the ID of your Google Cloud project.
   • LOCATION: for global external Application Load Balancers or classic Application Load Balancers, andcross-region internal Application Load Balancers, use global. For regional external Application Load Balancer or regional internal Application Load Balancer, use the region where you configured the load balancer.
   • SERVER_TLS_POLICY_NAME: the name of the Client Authentication (ServerTLSPolicy) resource.
   • TARGET_PROXY_FILENAME: the name of the target proxy's configuration file in YAML format.

5. To import a target HTTPS proxy's configuration from a file, use the gcloud compute target-https-proxies import command.

   global

     gcloud compute target-https-proxies import TARGET_HTTPS_PROXY_NAME \
         --source=TARGET_PROXY_FILENAME \
         --global
     

   Replace the following:

   • TARGET_HTTPS_PROXY_NAME: the name of the target proxy.
   • TARGET_PROXY_FILENAME: the name of the target proxy's configuration file in YAML format. For example, mtls_target_proxy.yaml.

   regional

     gcloud compute target-https-proxies import TARGET_HTTPS_PROXY_NAME \
         --source=TARGET_PROXY_FILENAME \
         --region=REGION
     

   Replace the following:

   • TARGET_HTTPS_PROXY_NAME: the name of the target proxy.
   • TARGET_PROXY_FILENAME: the name of the target proxy's configuration file in YAML format. For example, mtls_target_proxy.yaml
   • REGION: the region where you configured the load balancer.

Add mTLS custom headers

When you enable mTLS, you can pass information about the mTLS connection using custom headers. You can also enable logging so that mTLS connection failures are captured in the logs.

Add mTLS custom headers to backend services

For global external Application Load Balancers or classic Application Load Balancers, you can use custom headers to pass information about the mTLS connection to backend services.

1. To list all the backend services in the project, use the gcloud compute backend-services list command:

   gcloud compute backend-services list
   

   Note the name of the backend service to enable custom headers and logging. This name is referred to as BACKEND_SERVICE in the following step.

2. To update the backend service, use the gcloud compute backend-services update command:

   gcloud compute backend-services update BACKEND_SERVICE \
     --global \
     --enable-logging \
     --logging-sample-rate=1 \
     --custom-request-header='X-Client-Cert-Present:{client_cert_present}' \
     --custom-request-header='X-Client-Cert-Chain-Verified:{client_cert_chain_verified}' \
     --custom-request-header='X-Client-Cert-Error:{client_cert_error}' \
     --custom-request-header='X-Client-Cert-Hash:{client_cert_sha256_fingerprint}' \
     --custom-request-header='X-Client-Cert-Serial-Number:{client_cert_serial_number}' \
     --custom-request-header='X-Client-Cert-SPIFFE:{client_cert_spiffe_id}' \
     --custom-request-header='X-Client-Cert-URI-SANs:{client_cert_uri_sans}' \
     --custom-request-header='X-Client-Cert-DNSName-SANs:{client_cert_dnsname_sans}' \
     --custom-request-header='X-Client-Cert-Valid-Not-Before:{client_cert_valid_not_before}' \
     --custom-request-header='X-Client-Cert-Valid-Not-After:{client_cert_valid_not_after}'
   

Note:

You can provide your own custom header names. The names used in the --custom-request-header options are just examples.

You can enable some or all of the mTLS custom headers.

Add mTLS custom headers to URL map

For cross-region internal Application Load Balancer, regional external Application Load Balancer, or regional internal Application Load Balancer, you can use custom headers to pass information about the mTLS connection to the URL map.

To list all the URL maps in the project, use the gcloud compute url-maps list command:

   gcloud compute url-maps list
   

Note the name of the URL map to enable custom headers and logging. This name is referred to as URL_MAP_NAME in the following step.

global

To edit the URL map for a cross-region internal Application Load Balancer, use the gcloud compute url-maps edit command:

   gcloud compute url-maps edit URL_MAP_NAME --global
   

Following is a sample YAML file that shows you how to use variables in custom request headers (requestHeadersToAdd). You can use the same variables to send custom response headers (responseHeadersToAdd).

   headerAction:
      requestHeadersToAdd:
      - headerName: "X-Client-Cert-Present"
        headerValue: "{client_cert_present}"
      - headerName: "X-Client-Cert-Chain-Verified"
        headerValue: "{client_cert_chain_verified}"
      - headerName: "X-Client-Cert-Error"
        headerValue: "{client_cert_error}"
      - headerName: "X-Client-Cert-Hash"
        headerValue: "{client_cert_sha256_fingerprint}"
      - headerName: "X-Client-Cert-Serial-Number"
        headerValue: "{client_cert_serial_number}"
      - headerName: "X-Client-Cert-SPIFFE"
        headerValue: "{client_cert_spiffe_id}"
      - headerName: "X-Client-Cert-URI-SANs"
        headerValue: "{client_cert_uri_sans}"
      - headerName: "X-Client-Cert-DNSName-SANs"
        headerValue: "{client_cert_dnsname_sans}"
      - headerName: "X-Client-Cert-Valid-Not-Before"
        headerValue: "{client_cert_valid_not_before}"
      - headerName: "X-Client-Cert-Valid-Not-After"
        headerValue: "{client_cert_valid_not_after}"
      - headerName: "X-Client-Cert-Issuer-Dn"
        headerValue: "{client_cert_issuer_dn}"
      - headerName: "X-Client-Cert-Subject-Dn"
        headerValue: "{client_cert_subject_dn}"
      - headerName: "X-Client-Cert-Leaf"
        headerValue: "{client_cert_leaf}"
      - headerName: "X-Client-Cert-Chain"
        headerValue: "{client_cert_chain}"
   

regional

To edit the URL map for a regional external Application Load Balancer or a regional internal Application Load Balancer, use the gcloud compute url-maps edit command:

   gcloud compute url-maps edit URL_MAP_NAME --region=REGION
   

Following is a sample YAML file that shows you how to use variables in custom request headers (requestHeadersToAdd). You can use the same variables to send custom response headers (responseHeadersToAdd).

   defaultService: regions/REGION/backendServices/BACKEND_SERVICE_1
      name: regional-lb-map
      region: region/REGION
   headerAction:
      requestHeadersToAdd:
      - headerName: "X-Client-Cert-Present"
        headerValue: "{client_cert_present}"
      - headerName: "X-Client-Cert-Chain-Verified"
        headerValue: "{client_cert_chain_verified}"
      - headerName: "X-Client-Cert-Error"
        headerValue: "{client_cert_error}"
      - headerName: "X-Client-Cert-Hash"
        headerValue: "{client_cert_sha256_fingerprint}"
      - headerName: "X-Client-Cert-Serial-Number"
        headerValue: "{client_cert_serial_number}"
      - headerName: "X-Client-Cert-SPIFFE"
        headerValue: "{client_cert_spiffe_id}"
      - headerName: "X-Client-Cert-URI-SANs"
        headerValue: "{client_cert_uri_sans}"
      - headerName: "X-Client-Cert-DNSName-SANs"
        headerValue: "{client_cert_dnsname_sans}"
      - headerName: "X-Client-Cert-Valid-Not-Before"
        headerValue: "{client_cert_valid_not_before}"
      - headerName: "X-Client-Cert-Valid-Not-After"
        headerValue: "{client_cert_valid_not_after}"
      - headerName: "X-Client-Cert-Issuer-Dn"
        headerValue: "{client_cert_issuer_dn}"
      - headerName: "X-Client-Cert-Subject-Dn"
        headerValue: "{client_cert_subject_dn}"
      - headerName: "X-Client-Cert-Leaf"
        headerValue: "{client_cert_leaf}"
      - headerName: "X-Client-Cert-Chain"
        headerValue: "{client_cert_chain}"
   

What's next

• Set up mutual TLS with signed certificates