228 lines
11 KiB
Text
228 lines
11 KiB
Text
## X.509 Client Certificate User Authentication
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Keycloak supports login with a X.509 client certificate if the server is configured for mutual SSL authentication.
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A typical workflow is as follows:
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- A client sends an authentication request over SSL/TLS channel
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- During SSL/TLS handshake, the server and the client exchange their x.509/v3 certificates
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- The container (wildfly) validates the certificate PKIX path and the certificate expiration
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- The x.509 client certificate authenticator validates the client certificate as follows:
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* Optionally checks the certificate revocation status using CRL and/or CRL Distribution Points
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* Optionally checks the Certificate revocation status using OCSP (Online Certificate Status Protocol)
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* Optinally validates whether the key usage in the certificate matches the expected key usage
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* Optionally validates whether the extended key usage in the certificate matches the expected extended key usage
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- If any of the above checks fails, the x.509 authentication fails
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- Otherwise, the authenticator extracts the certificate identity and maps it to an existing user
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- Once the certificate is mapped to an existing user, the behavior diverges depending on the authentication flow:
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* In the Browser Flow, the server prompts the user to confirm identity or to ignore it and instead sign in with username/password
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* In the case of the Direct Grant Flow, the server signs in the user
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### Features
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#### Supported Certificate Identity Sources
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- Match SubjectDN using regular expression
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- X500 Subject's e-mail attribute
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- X500 Subject's Common Name attribute
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- Match IssuerDN using regular expression
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- X500 Issuer's e-mail attribute
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- X500 Issuer's Common Name attribute
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- Certificate Serial Number
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#### Regular Expressions
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The certificate identity can be extracted from either Subject DN or Issuer DN using a regular expression as a filter. For example, the regular expression below will match the e-mail attribute:
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```
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emailAddress=(.*?)(?:,|$)
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```
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The regular expression filtering is applicable only if the `Identity Source` is set to either `Match SubjectDN using regular expression` or `Match IssuerDN using regular expression`.
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#### Mapping certificate identity to an existing user
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The certificate identity mapping can be configured to map the extracted user identity to an existing user's username or e-mail or to a custom attribute which value matches the certificate identity. For example, setting the `Identity source` to _Subject's e-mail_ and `User mapping method` to _Username or email_ will have the X.509 client certificate authenticator use the e-mail attribute in the certificate's Subject DN as a search criteria to look up an existing user by username or by e-mail.
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#### Other Features: Extended Certificate Validation
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- Revocation status checking using CRL
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- Revocation status checking using CRL/Distribution Point
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- Revocation status checking using OCSP/Responder URI
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- Certificate KeyUsage validation
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- Certificate ExtendedKeyUsage validation
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### Enable X.509 Client Certificate User Authentication
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The following sections describe how to configure Wildfly/Undertow and the Keycloak Server to enable X.509 client certificate authentication.
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#### Enable mutual SSL in WildFly
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See link:https://docs.jboss.org/author/display/WFLY10/Admin+Guide#AdminGuide-EnableSSL[Enable SSL] and link:https://docs.jboss.org/author/display/WFLY10/Admin+Guide#AdminGuide-%7B%7B%3Cssl%2F%3E%7D%7D[SSL] for the instructions how to enable SSL in Wildfly.
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* Open $KEYCLOAK_HOME/standalone/configuration/standalone.xml and add a new realm:
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```
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<security-realms>
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<security-realm name="ssl-realm">
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<server-identities>
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<ssl>
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<keystore path="servercert.jks"
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relative-to="jboss.server.config.dir"
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keystore-password="servercert password"/>
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</ssl>
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</server-identities>
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<authentication>
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<truststore path="truststore.jks"
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relative-to="jboss.server.config.dir"
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keystore-password="truststore password"/>
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</authentication>
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</security-realm>
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</security-realms>
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```
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`ssl/keystore`::
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The `ssl` element contains the `keystore` element that defines how to load the server public key pair from a JKS keystore
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`ssl/keystore/path`::
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A path to a JKS keystore
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`ssl/keystore/relative-to`::
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Defines a path the keystore path is relative to
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`ssl/keystore/keystore-password`::
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The password to open the keystore
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`ssl/keystore/alias` (optional)::
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The alias of the entry in the keystore. Set it if the keystore contains multiple entries
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`ssl/keystore/key-password` (optional)::
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The private key password, if different from the keystore password.
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`authentication/truststore`::
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Defines how to load a trust store to verify the certificate presented by the remote side of the inbound/outgoing connection. Typically, the truststore contains a collection of trusted CA certificates.
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`authentication/truststore/path`::
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A path to a JKS keystore that contains the certificates of the trusted CAs (certificate authorities)
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`authentication/truststore/relative-to`::
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Defines a path the truststore path is relative to
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`authentication/truststore/keystore-password`::
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The password to open the truststore
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#### Enable https listener
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See link:https://docs.jboss.org/author/display/WFLY10/Admin+Guide#AdminGuide-HTTPSlistener[HTTPS Listener] for the instructions how to enable HTTPS in Wildfly.
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* Add the <https-listener> element as shown below:
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[source,xml,subs="attributes+"]
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----
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<subsystem xmlns="{subsystem_undertow_xml_urn}">
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....
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<server name="default-server">
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<https-listener name="default"
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socket-binding="https"
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security-realm="ssl-realm"
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verify-client="REQUESTED"/>
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</server>
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</subsystem>
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----
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`https-listener/security-realm`::
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The value must match the name of the realm from the previous section
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`https-listener/verify-client`::
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If set to `REQUESTED`, the server will optionally ask for a client certificate. Setting the attribute to `REQUIRED` will have the server to refuse inbound connections if no client certificate has been provided.
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### Adding X.509 Client Certificate Authentication to a Browser Flow
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* Select a realm, click on Authentication link, select the "Browser" flow
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* Make a copy of the buit-in "Browser" flow. You may want to give the new flow a distinctive name, i.e. "X.509 Browser"
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* Using the drop down, select the copied flow, and click on "Add Execution"
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* Select "X509/Validate User Form" using the drop down and click on "Save"
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image:{project_images}/x509-execution.png[]
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* Using the up/down arrows, change the order of the "X509/Validate Username Form" by moving it above the "Browser Forms" execution, and set the requirement to "ALTERNATIVE"
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image:{project_images}/x509-browser-flow.png[]
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#### Configuring X.509 Client Certificate Authentication
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image:{project_images}/x509-configuration.png[]
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`User Identity Source`::
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Defines how to extract the user identity from a client certificate.
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`A regular expression` (optional)::
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Defines a regular expression to use as a filter to extract the certificate identity. The regular expression must contain a single group.
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`User Mapping Method`::
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Defines how to match the certificate identity to an existing user. _Username or e-mail_ will search for an existing user by username or e-mail. _Custom Attribute Mapper_ will search for an existing user with a custom attribute which value matches the certificate identity. The name of the custom attribute is configurable.
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`A name of user attribute` (optional)::
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A custom attribute which value will be matched against the certificate identity.
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`CRL Checking Enabled` (optional)::
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Defines whether to check the revocation status of the certificate using Certificate Revocation List.
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`Enable CRL Distribution Point to check certificate revocation status` (optional)::
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Defines whether to use CDP to check the certificate revocation status. Most PKI authorities include CDP in their certificates.
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`CRL file path` (optional)::
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Defines a path to a file that contains a CRL list. The value must be a path to a valid file if `CRL Checking Enabled` option is turned on.
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`OCSP Checking Enabled`(optional)::
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Defines whether to check the certificate revocation status using Online Certificate Status Protocol.
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`OCSP Responder URI` (optional)::
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Allows to override a value of the OCSP responder URI in the certificate.
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`Validate Key Usage` (optional)::
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Verifies whether the certificate's KeyUsage extension bits are set. For example, "digitalSignature,KeyEncipherment" will verify if bits 0 and 2 in the KeyUsage extension are asserted. Leave the parameter empty to disable the Key Usage validaion. See link:https://tools.ietf.org/html/rfc5280#section-4.2.1.3[RFC5280, Section-4.2.1.3]
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`Validate Extended Key Usage` (optional)::
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Verifies one or more purposes as defined in the Extended Key Usage extension. See link:https://tools.ietf.org/html/rfc5280#section-4.2.1.12[RFC5280, Section-4.2.1.12]. Leave the parameter empty to disable the Extended Key Usage validation.
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`Bypass identity confirmation`::
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If set, X.509 client certificate authentication will not prompt the user to confirm the certificate identity and will automatiocally sign in the user upon successful authentication.
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### Adding X.509 Client Certificate Authentication to a Direct Grant Flow
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* Using keycloak admin console, click on "Authentication" and select the "Direct Grant" flow,
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* Make a copy of the build-in "Direct Grant" flow. You may want to give the new flow a distinctive name, i.e. "X509 Direct Grant",
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* Delete "Validate Username" and "Password" authenticators,
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* Click on "Execution" and add "X509/Validate Username" and click on "Save" to add the execution step to the parent flow.
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image:{project_images}/x509-directgrant-execution.png[]
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* Change the `Requirement` to _REQUIRED_.
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image:{project_images}/x509-directgrant-flow.png[]
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* Set up the x509 authentication configuration by following the steps described earlier in the x.509 Browser Flow section.
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### Troubleshooting
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#### Direct Grant authentication with X.509
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The following template can be used to request a token using the Resource Owner Password Credentials Grant:
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```
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$ curl https://[host][:port]/auth/realms/master/protocol/openid-connect/token \
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--insecure \
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--data "grant_type=password&scope=openid profile&username=&password=&client_id=CLIENT_ID&client_secret=CLIENT_SECRET" \
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-E /path/to/client_cert.crt \
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--key /path/to/client_cert.key
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```
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`[host][:port]`::
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The host and the port number of a remote Keycloak server that has been configured to allow users authenticate with x.509 client certificates using the Direct Grant Flow.
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`CLIENT_ID`::
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A client id.
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`CLIENT_SECRET`::
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For confidential clients, a client secret; otherwise, leave it empty.
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`client_cert.crt`::
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A public key certificate that will be used to verify the identity of the client in mutual SSL authentication. The certificate should be in PEM format.
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`client_cert.key`::
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A private key in the public key pair. Also expected in PEM format.
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