API Management policies for GraphQL APIs

This article provides a reference for API Management policies to validate and resolve queries to GraphQL APIs.

More information about policies:

GraphQL API policies

Validate GraphQL request

The validate-graphql-request policy validates the GraphQL request and authorizes access to specific query paths. An invalid query is a "request error". Authorization is only done for valid requests.

Permissions
Because GraphQL queries use a flattened schema:

  • Permissions may be applied at any leaf node of an output type:
    • Mutation, query, or subscription
    • Individual field in a type declaration.
  • Permissions may not be applied to:
    • Input types
    • Fragments
    • Unions
    • Interfaces
    • The schema element

Authorize element
Configure the authorize element to set an appropriate authorization rule for one or more paths.

  • Each rule can optionally provide a different action.
  • Use policy expressions to specify conditional actions.

Introspection system
The policy for path=/__* is the introspection system. You can use it to reject introspection requests (__schema, __type, etc.).

Note

Set the policy's elements and child elements in the order provided in the policy statement. Learn more about how to set or edit API Management policies.

Policy statement

<validate-graphql-request error-variable-name="variable name" max-size="size in bytes" max-depth="query depth">
    <authorize>
        <rule path="query path, for example: '/listUsers' or '/__*'" action="string or policy expression that evaluates to 'allow|remove|reject|ignore'" />
    </authorize>
</validate-graphql-request>

Example: Query validation

This example applies the following validation and authorization rules to a GraphQL query:

  • Requests larger than 100 kb or with query depth greater than 4 are rejected.
  • Requests to the introspection system are rejected.
  • The /Missions/name field is removed from requests containing more than two headers.
<validate-graphql-request error-variable-name="name" max-size="102400" max-depth="4"> 
    <authorize>
        <rule path="/__*" action="reject" /> 
        <rule path="/Missions/name" action="@(context.Request.Headers.Count > 2 ? "remove" : "allow")" />
    </authorize>
</validate-graphql-request> 

Example: Mutation validation

This example applies the following validation and authorization rules to a GraphQL mutation:

  • Requests larger than 100 kb or with query depth greater than 4 are rejected.
  • Requests to mutate the deleteUser field are denied except when the request is from IP address 198.51.100.1.
<validate-graphql-request error-variable-name="name" max-size="102400" max-depth="4"> 
    <authorize>
        <rule path="/Mutation/deleteUser" action="@(context.Request.IpAddress <> "198.51.100.1" ? "deny" : "allow")" />
    </authorize>
</validate-graphql-request> 

Elements

Name Description Required
validate-graphql-request Root element. Yes
authorize Add this element to provide field-level authorization with both request- and field-level errors. No
rule Add one or more of these elements to authorize specific query paths. Each rule can optionally specify a different action. No

Attributes

Name Description Required Default
error-variable-name Name of the variable in context.Variables to log validation errors to. No N/A
max-size Maximum size of the request payload in bytes. Maximum allowed value: 102,400 bytes (100 KB). (Contact support if you need to increase this limit.) Yes N/A
max-depth An integer. Maximum query depth. No 6
path Path to execute authorization validation on. It must follow the pattern: /type/field. Yes N/A
action Action to perform if the rule applies. May be specified conditionally using a policy expression. No allow

Request actions

Available actions are described in the following table.

Action Description
reject A request error happens, and the request is not sent to the back end. Additional rules if configured are not applied.
remove A field error happens, and the field is removed from the request.
allow The field is passed to the back end.
ignore The rule is not valid for this case and the next rule is applied.

Error handling

Failure to validate against the GraphQL schema, or a failure for the request's size or depth, is a request error and results in the request being failed with an errors block (but no data block).

Similar to the Context.LastError property, all GraphQL validation errors are automatically propagated in the GraphQLErrors variable. If the errors need to be propagated separately, you can specify an error variable name. Errors are pushed onto the error variable and the GraphQLErrors variable.

Usage

This policy can be used in the following policy sections and scopes.

  • Policy sections: inbound

  • Policy scopes: all scopes

Set GraphQL resolver

The set-graphql-resolver policy retrieves or sets data for a GraphQL field in an object type specified in a GraphQL schema. The schema must be imported to API Management. Currently the data must be resolved using an HTTP-based data source (REST or SOAP API).

Important

Configuring resolvers for GraphQL queries is currently in preview. This feature is not available in the Consumption service tier or in the self-hosted gateway.

  • This policy is invoked only when a matching GraphQL query is executed.
  • The policy resolves data for a single field. To resolve data for multiple fields, configure multiple occurrences of this policy in a policy definition.

Note

Set the policy's elements and child elements in the order provided in the policy statement. Learn more about how to set or edit API Management policies.

Policy statement

<set-graphql-resolver parent-type="type" field="field"> 
    <http-data-source> 
        <http-request> 
            <set-method>...set-method policy configuration...</set-method> 
            <set-url>URL</set-url>
            <set-header>...set-header policy configuration...</set-header>
            <set-body>...set-body policy configuration...</set-body>
            <authentication-certificate>...authentication-certificate policy configuration...</authentication-certificate>  
        </http-request> 
        <http-response>
            <json-to-xml>...json-to-xml policy configuration...</json-to-xml>
            <xml-to-json>...xml-to-json policy configuration...</xml-to-json>
            <find-and-replace>...find-and-replace policy configuration...</find-and-replace>
        </http-response>
      </http-data-source> 
</set-graphql-resolver> 

Elements

Name Description Required
set-graphql-resolver Root element. Yes
http-data-source Configures the HTTP request and optionally the HTTP response that are used to resolve data for the given parent-type and field. Yes
http-request Specifies a URL and child policies to configure the resolver's HTTP request. Each child element can be specified at most once. Yes
set-method Method of the resolver's HTTP request, configured using the set-method policy. Yes
set-url URL of the resolver's HTTP request. Yes
set-header Header set in the resolver's HTTP request, configured using the set-header policy. No
set-body Body set in the resolver's HTTP request, configured using the set-body policy. No
authentication-certificate Client certificate presented in the resolver's HTTP request, configured using the authentication-certificate policy. No
http-response Optionally specifies child policies to configure the resolver's HTTP response. If not specified, the response is returned as a raw string. Each child element can be specified at most once.
json-to-xml Transforms the resolver's HTTP response using the json-to-xml policy. No
xml-to-json Transforms the resolver's HTTP response using the xml-to-json policy. No
find-and-replace Transforms the resolver's HTTP response using the find-and-replace policy. No

Attributes

Name Description Required Default
parent-type An object type in the GraphQL schema. Yes N/A
field A field of the specified parent-type in the GraphQL schema. Yes N/A

Note

Currently, the values of parent-type and field aren't validated by this policy. If they aren't valid, the policy is ignored, and the GraphQL query is forwarded to a GraphQL endpoint (if one is configured).

Usage

This policy can be used in the following policy sections and scopes.

  • Policy sections: backend
  • Policy scopes: all scopes

GraphQL Context

  • The context for the HTTP request and HTTP response (if specified) differs from the context for the original gateway API request:
    • context.ParentResult is set to the parent object for the current resolver execution.
    • The HTTP request context contains arguments that are passed in the GraphQL query as its body.
    • The HTTP response context is the response from the independent HTTP call made by the resolver, not the context for the complete response for the gateway request. The context variable that is passed through the request and response pipeline is augmented with the GraphQL context when used with <set-graphql-resolver> policies.

ParentResult

The context.ParentResult is set to the parent object for the current resolver execution. Consider the following partial schema:

type Comment {
    id: ID!
    owner: string!
    content: string!
}

type Blog {
    id: ID!
    title: string!
    content: string!
    comments: [Comment]!
    comment(id: ID!): Comment
}

type Query {
    getBlog(): [Blog]!
    getBlog(id: ID!): Blog
}

Also, consider a GraphQL query for all the information for a specific blog:

query {
    getBlog(id: 1) {
        title
        content
        comments {
            id
            owner
            content
        }
    }
}

If you set a resolver for parent-type="Blog" field="comments", you will want to understand which blog ID to use. You can get the ID of the blog using context.ParentResult.AsJObject()["id"].ToString(). The policy for configuring this resolver would resemble:

<set-graphql-resolver parent-type="Blog" field="comments">
    <http-data-source>
        <http-request>
            <set-method>GET</set-method>
            <set-url>@{
                var blogId = context.ParentResult.AsJObject()["id"].ToString();
                return $"https://data.contoso.com/api/blog/{blogId}";
            }</set-url>
        </http-request>
    </http-data-source>
</set-graphql-resolver>

Arguments

The arguments for a parameterized GraphQL query are added to the body of the request. For example, consider the following two queries:

query($id: Int) {
    getComment(id: $id) {
        content
    }
}

query {
    getComment(id: 2) {
        content
    }
}

These queries are two ways of calling the getComment resolver. GraphQL sends the following JSON payload:

{
    "query": "query($id: Int) { getComment(id: $id) { content } }",
    "variables": { "id": 2 }
}

{
    "query": "query { getComment(id: 2) { content } }"
}

When the resolver is executed, the arguments property is added to the body. You can define the resolver as follows:

<set-graphql-resolver parent-type="Blog" field="comments">
    <http-data-source>
        <http-request>
            <set-method>GET</set-method>
            <set-url>@{
                var commentId = context.Request.Body.As<JObject>(true)["arguments"]["id"];
                return $"https://data.contoso.com/api/comment/{commentId}";
            }</set-url>
        </http-request>
    </http-data-source>
</set-graphql-resolver>

More examples

Resolver for GraphQL query

The following example resolves a query by making an HTTP GET call to a backend data source.

Example schema
type Query {
    users: [User]
}

type User {
    id: String!
    name: String!
}
Example policy
<set-graphql-resolver parent-type="Query" field="users">
    <http-data-source>
        <http-request>
            <set-method>GET</set-method>
            <set-url>https://data.contoso.com/get/users</set-url>
        </http-request>
    </http-data-source>
</set-graphql-resolver>

Resolver for a GraqhQL query that returns a list, using a liquid template

The following example uses a liquid template, supported for use in the set-body policy, to return a list in the HTTP response to a query. It also renames the username field in the response from the REST API to name in the GraphQL response.

Example schema
type Query {
    users: [User]
}

type User {
    id: String!
    name: String!
}
Example policy
<set-graphql-resolver parent-type="Query" field="users">
    <http-data-source>
        <http-request>
            <set-method>GET</set-method>
            <set-url>https://data.contoso.com/users</set-url>
        </http-request>
        <http-response>
            <set-body template="liquid">
                [
                    {% JSONArrayFor elem in body %}
                        {
                            "name": "{{elem.username}}"
                        }
                    {% endJSONArrayFor %}
                ]
            </set-body>
        </http-response>
    </http-data-source>
</set-graphql-resolver>

Resolver for GraphQL mutation

The following example resolves a mutation that inserts data by making a POST request to an HTTP data source. The policy expression in the set-body policy of the HTTP request modifies a name argument that is passed in the GraphQL query as its body. The body that is sent will look like the following JSON:

{
    "name": "the-provided-name"
}
Example schema
type Query {
    users: [User]
}

type Mutation {
    makeUser(name: String!): User
}

type User {
    id: String!
    name: String!
}
Example policy
<set-graphql-resolver parent-type="Mutation" field="makeUser">
    <http-data-source>
        <http-request>
            <set-method>POST</set-method>
            <set-url> https://data.contoso.com/user/create </set-url>
            <set-header name="Content-Type" exists-action="override">
                <value>application/json</value>
            </set-header>
            <set-body>@{
                var args = context.Request.Body.As<JObject>(true)["arguments"];  
                JObject jsonObject = new JObject();
                jsonObject.Add("name", args["name"])
                return jsonObject.ToString();
            }</set-body>
        </http-request>
    </http-data-source>
</set-graphql-resolver>

Next steps

For more information about working with policies, see: