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validate-content-policy.md

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Azure API Management policy reference - validate-content | Microsoft Docs
Reference for the validate-content policy available for use in Azure API Management. Provides policy usage, settings, and examples.
api-management
dlepow
api-management
article
03/18/2024
danlep

Validate content

[!INCLUDE api-management-availability-all-tiers]

The validate-content policy validates the size or content of a request or response body against one or more supported schemas.

The following table shows the schema formats and request or response content types that the policy supports. Content type values are case insensitive.

Format Content types
JSON Examples: application/json
application/hal+json
XML Example: application/xml
SOAP Allowed values: application/soap+xml for SOAP 1.2 APIs
text/xml for SOAP 1.1 APIs

[!INCLUDE api-management-validation-policy-schema-size-note]

What content is validated

The policy validates the following content in the request or response against the schema:

  • Presence of all required properties.
  • Presence or absence of additional properties, if the schema has the additionalProperties field set. May be overridden with the allow-additional-properties attribute.
  • Types of all properties. For example, if a schema specifies a property as an integer, the request (or response) must include an integer and not another type, such as a string.
  • The format of the properties, if specified in the schema - for example, regex (if the pattern keyword is specified), minimum for integers, and so on.

Tip

For examples of regex pattern constraints that can be used in schemas, see OWASP Validation Regex Repository.

[!INCLUDE api-management-policy-form-alert]

Policy statement

<validate-content unspecified-content-type-action="ignore | prevent | detect" max-size="size in bytes" size-exceeded-action="ignore | prevent | detect" errors-variable-name="variable name">
    <content-type-map any-content-type-value="content type string" missing-content-type-value="content type string">
        <type from | when="content type string" to="content type string" />
    </content-type-map>
    <content type="content type string" validate-as="json | xml | soap" schema-id="schema id" schema-ref="#/local/reference/path" action="ignore | prevent | detect" allow-additional-properties="true | false" />
</validate-content>

Attributes

Attribute Description Required Default
unspecified-content-type-action Action to perform for requests or responses with a content type that isn’t specified in the API schema. Policy expressions are allowed. Yes N/A
max-size Maximum length of the body of the request or response in bytes, checked against the Content-Length header. If the request body or response body is compressed, this value is the decompressed length. Maximum allowed value: 102,400 bytes (100 KB). (Contact support if you need to increase this limit.) Policy expressions are allowed. Yes N/A
size-exceeded-action Action to perform for requests or responses whose body exceeds the size specified in max-size. Policy expressions are allowed. Yes N/A
errors-variable-name Name of the variable in context.Variables to log validation errors to. Policy expressions aren't allowed. No N/A

Elements

Name Description Required
content-type-map Add this element to map the content type of the incoming request or response to another content type that is used to trigger validation. No
content Add one or more of these elements to validate the content type in the request or response, or the mapped content type, and perform the specified action. No

content-type-map attributes

Attribute Description Required Default
any-content-type-value Content type used for validation of the body of a request or response, regardless of the incoming content type. Policy expressions aren't allowed. No N/A
missing-content-type-value Content type used for validation of the body of a request or response, when the incoming content type is missing or empty. Policy expressions aren't allowed. No N/A

content-type-map-elements

Name Description Required
type Add one or more of these elements to map an incoming content type to a content type used for validation of the body of a request or response. Use from to specify a known incoming content type, or use when with a policy expression to specify any incoming content type that matches a condition. Overrides the mapping in any-content-type-value and missing-content-type-value, if specified. No

content attributes

Attribute Description Required Default
type Content type to execute body validation for, checked against the content type header or the value mapped in content-type-mapping, if specified. If empty, it applies to every content type specified in the API schema.

To validate SOAP requests and responses (validate-as attribute set to "soap"), set type to application/soap+xml for SOAP 1.2 APIs or text/xml for SOAP 1.1 APIs.		 No N/A
validate-as Validation engine to use for validation of the body of a request or response with a matching type. Supported values: "json", "xml", "soap".

When "soap" is specified, the XML from the request or response is extracted from the SOAP envelope and validated against an XML schema.		 Yes N/A
schema-id Name of an existing schema that was added to the API Management instance for content validation. If not specified, the default schema from the API definition is used. No N/A
schema-ref For a JSON schema specified in schema-id, optional reference to a valid local reference path in the JSON document. Example: #/components/schemas/address. The attribute should return a JSON object that API Management handles as a valid JSON schema.

For an XML schema, schema-ref isn't supported, and any top-level schema element can be used as the root of the XML request or response payload. The validation checks that all elements starting from the XML request or response payload root adhere to the provided XML schema.		 No N/A
allow-additional-properties Boolean. For a JSON schema, specifies whether to implement a runtime override of the additionalProperties value configured in the schema:
- true: allow additional properties in the request or response body, even if the JSON schema's additionalProperties field is configured to not allow additional properties.
- false: do not allow additional properties in the request or response body, even if the JSON schema's additionalProperties field is configured to allow additional properties.

If the attribute isn't specified, the policy validates additional properties according to configuration of the additionalProperties field in the schema.		 No N/A

[!INCLUDE api-management-validation-policy-actions]

Usage

[!INCLUDE api-management-validation-policy-common]

Schemas for content validation

By default, validation of request or response content uses JSON or XML schemas from the API definition. These schemas can be specified manually or generated automatically when importing an API from an OpenAPI or WSDL specification into API Management.

Using the validate-content policy, you may optionally validate against one or more JSON or XML schemas that you’ve added to your API Management instance and that aren't part of the API definition. A schema that you add to API Management can be reused across many APIs.

To add a schema to your API Management instance using the Azure portal:

  1. In the portal, navigate to your API Management instance.

  2. In the APIs section of the left-hand menu, select Schemas > + Add.

  3. In the Create schema window, do the following:

    1. Enter a Name (ID) for the schema.
    2. In Schema type, select JSON or XML.
    3. Enter a Description.
    4. In Create method, do one of the following:
      • Select Create new and enter or paste the schema.
      • Select Import from file or Import from URL and enter a schema location.

        [!NOTE] To import a schema from URL, the schema needs to be accessible over the internet from the browser.

    5. Select Save.

    :::image type="content" source="media/validation-policies/add-schema.png" alt-text="Create schema":::

API Management adds the schema resource at the relative URI /schemas/<schemaId>, and the schema appears in the list on the Schemas page. Select a schema to view its properties or to edit in a schema editor.

Note

A schema may cross-reference another schema that is added to the API Management instance. For example, include an XML schema added to API Management by using an element similar to:

<xs:include schemaLocation="/schemas/myschema" />

Tip

Open-source tools to resolve WSDL and XSD schema references and to batch-import generated schemas to API Management are available on GitHub.

Examples

JSON schema validation

In the following example, API Management interprets requests with an empty content type header or requests with a content type header application/hal+json as requests with the content type application/json. Then, API Management performs the validation in the detection mode against a schema defined for the application/json content type in the API definition. Messages with payloads larger than 100 KB are blocked. Requests containing additional properties are blocked, even if the schema's additionalProperties field is configured to allow additional properties.

<validate-content unspecified-content-type-action="prevent" max-size="102400" size-exceeded-action="prevent" errors-variable-name="requestBodyValidation">
    <content-type-map missing-content-type-value="application/json">
        <type from="application/hal+json" to="application/json" />
    </content-type-map>
    <content type="application/json" validate-as="json" action="detect" allow-additional-properties="false" />
</validate-content>

SOAP schema validation

In the following example, API Management interprets any request as a request with the content type application/soap+xml (the content type that's used by SOAP 1.2 APIs), regardless of the incoming content type. The request could arrive with an empty content type header, content type header of text/xml (used by SOAP 1.1 APIs), or another content type header. Then, API Management extracts the XML payload from the SOAP envelope and performs the validation in prevention mode against the schema named "myschema". Messages with payloads larger than 100 KB are blocked.

<validate-content unspecified-content-type-action="prevent" max-size="102400" size-exceeded-action="prevent" errors-variable-name="requestBodyValidation">
    <content-type-map any-content-type-value="application/soap+xml" />
    <content type="application/soap+xml" validate-as="soap" schema-id="myschema" action="prevent" /> 
</validate-content>

[!INCLUDE api-management-validation-policy-error-reference]

Related policies

[!INCLUDE api-management-policy-ref-next-steps]