Transport Layer Security Policy - Outbound | MuleSoft Documentation
# Transport Layer Security Policy - Outbound
**Policy Name** |  Transport Layer Security (TLS) - Outbound  
---|---  
Enables two-way authentication between the API proxy and an upstream service  
**First Flex version available**  
**Returned Status Codes** |  No return codes exist for this policy.  
The following document applies only to Flex Gateway running in Local Mode. To configure TLS in Connected Mode, see Configuring TLS Context for Flex Gateway in Connected Mode.  
---  
## Summary
Flex Gateway supports outbound Transport Layer Security (TLS) and outbound mutual authentication TLS (mTLS) in Local Mode.
By default, Flex Gateway supports outbound TLS to communicate with upstream services that require a secure communication channel. For default outbound communication, Flex Gateway uses only TLS 1.2. To find the default TLS 1.2 ciphers, see Flex Gateway Supported Ciphers. To find the ciphers, see Flex Gateway Supported Ciphers. Applying a TLS context to an upstream overrides the default TLS context for that upstream. Because the default ciphers may change for later Flex Gateway versions, you can apply a TLS context to an upstream to ensure it remains the same.
To apply outbound TLS in Local Mode, use the Configuring TLS Context for Flex Gateway in Local Mode tutorial and refer to the following configuration files in this documentation.
You can configure an outbound TLS context to enable authentication between an API instance and an upstream service by binding the TLS policy to the upstream service.
Unlike inbound TLS, it is not suggested to apply the same outbound TLS context to all API instances in your Flex Gateway because your API upstream services might come from different providers. Therefore, no configuration example for outbound TLS on all instances is provided.
Port sharing is not a concern for outbound TLS. You can apply an outbound TLS context for each individual upstream service.
TLS policies do not support policy ordering.  
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Upstream certificates must include the Subject Alternative Name (SAN) extension. The Common Name (CN) field is deprecated. Flex Gateway supports the SAN extension of type `dNSName`.  
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The Authority Information Access (AIA) certificate extension is not supported when configuring outbound TLS contexts.  
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## Configuring Policy Parameters
To enable outbound TLS between an API instance and an upstream service when using Flex Gateway as your runtime, you must manually configure the TLS context in a YAML configuration file.
Refer to the following policy definition and table of parameters:
```
- policyRef:
  name: tls-outbound
 config:
  skipValidation: <boolean> // REQUIRED
  certificate: // OPTIONAL
    key: <string> // OPTIONAL
    crt: <string> // OPTIONAL
  alpn: <array> // OPTIONAL
  minversion: <string> // OPTIONAL
  maxversion: <string> // OPTIONAL
  ciphers: <array> // OPTIONAL
```

Not including optional parameters in your configuration file applies the parameters default values to your TLS context.
When configuring the `ciphers` parameter, ensure that your API upstream supports the listed ciphers. For the supported ciphers, see TLS Cipher Support on Flex Gateway.
Parameter | Required or Optional | Default Value | Description  
---|---|---|---  
`skipValidation` |  Skipping validation disables outbound mTLS  
Optional, unless `skipValidation` is false |  The client certificate used in mTLS  
A TLS certificate key pair. To comply with security standards, all certificates must be 2048 bits or longer.  
`certificate.key` |  The private key part of the certificate  
`certificate.crt` |  The public key part of the certificate  
`h2` and `http/1.1` |  A prioritized list of supported application level protocols; for example, h2, http/1.1, and so forth.  
The minimum TLS version allowed  
The maximum TLS version allowed  
For the default and other supported ciphers, see TLS Cipher Support on Flex Gateway. |  A list of supported TLS ciphers (IANA format).  
### Resource Configuration Examples
You can format the YAML file to configure TLS or mTLS for a upstream service.
**Sample configuration for adding outbound TLS context for a specific upstream service:**
```
apiVersion: gateway.mulesoft.com/v1alpha1
kind: PolicyBinding
metadata:
 name: tls-outbound
spec:
 targetRef:
  kind: Service
  name: ingress-test-outbound-upstream
 policyRef:
  name: tls-outbound
 config:
  skipValidation: true
  certificate:
   key: |
    # -----BEGIN PRIVATE KEY-----
    # insert certificate key
    # -----END PRIVATE KEY-----
   crt: |
    # -----BEGIN CERTIFICATE-----
    # insert certificate
    # -----END CERTIFICATE-----
```

This example uses the default values for `alpn`, `minversion`, `maxversion`, and `ciphers`.
**Sample configuration for adding outbound mTLS context for a specific upstream service:**
```
apiVersion: gateway.mulesoft.com/v1alpha1
kind: PolicyBinding
metadata:
 name: mtls-outbound
spec:
 targetRef:
  kind: Service
  name: ingress-test-outbound-upstream
 policyRef:
  name: tls-outbound
 config:
  skipValidation: false
  trustedCA: |
   # -----BEGIN CERTIFICATE-----
   # insert certificate
   # -----END CERTIFICATE-----
  certificate:
   key: |
    # -----BEGIN PRIVATE KEY-----
    # insert certificate key
    # -----END PRIVATE KEY-----
   crt: |
    # -----BEGIN CERTIFICATE-----
    # insert certificate
    # -----END CERTIFICATE-----
  alpn:
   - http/1.1
   - h2
  minversion: "1.1"
  maxversion: "1.3"
  ciphers:
   - TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
   - TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256
   - TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
   - TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
   - TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
   - TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
```

## TLS Cipher Support on Flex Gateway
Flex can support a range of TLS Versions from TLS 1.1 to TLS 1.3, and you can also customize some of the ciphers to support.
You cannot customize the list of TLS 1.3 Ciphers. If you support TLS 1.3, the TLS 1.3 default ciphers are all supported regardless of the ciphers listed in the configuration file. If you don’t support TLS 1.3, these ciphers are not included.
For TLS 1.2, listing any ciphers overides the TLS 1.2 default ciphers. If you want to list ciphers besides the default TLS 1.2 Ciphers, you must list every cipher to support including the default ciphers you want to support. Excluding default ciphers from your list of supported ciphers means you do not support those ciphers. If you wish to only support the default ciphers, you can leave the cipher list blank. Listing ciphers does not affect the default TLS 1.3 cipher.
There are no default ciphers for TLS 1.1. To support TLS 1.1, you must list the ciphers to support. If you support TLS 1.1 and TLS 1.2, listing TLS 1.1 ciphers overides the TLS 1.2 defaults. To support both these versions, list all ciphers you want to support.
For outbound TLS Context, ensure that your upstream service supports the selected ciphers and versions.   
---  
### Flex Gateway Supported Ciphers
Flex Gateway supports the following TLS Ciphers in Connected Mode and Local Mode:
Cipher | TLS Version | Default | Advice  
---|---|---|---  
TLS_AES_128_GCM_SHA256  
TLS_AES_256_GCM_SHA384  
TLS_CHACHA20_POLY1305_SHA256  
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 |  Recommended  
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 |  Recommended  
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 |  Recommended  
TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256 |  Recommended  
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256  
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384  
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256  
TLS_RSA_WITH_AES_128_GCM_SHA256  
TLS_RSA_WITH_AES_256_GCM_SHA384  
TLS_RSA_WITH_AES_128_CBC_SHA  
TLS_RSA_WITH_AES_256_CBC_SHA  
TLS_PSK_WITH_AES_128_CBC_SHA  
TLS_PSK_WITH_AES_256_CBC_SHA  
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA  
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA  
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA  
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA  
TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA  
TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA  
TLS_RSA_WITH_3DES_EDE_CBC_SHA  
## See Also
  * Configuring TLS Context for Flex Gateway in Connected Mode
  * Configuring TLS Context for Flex Gateway in Local Mode
  * Transport Layer Security Policy - Inbound