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Dotnet Core GraphQL API Authorization

Introduction:

GraphQL API Authorization can be done by implementing GraphQL.Validation.IValidationRule. By implementing IValidationRule we have to implement our own custom rules for validating queries. So we can implement our own custom logic for authorization. IValidationRule is the perfect way of implementing authorization because these rules always get executed prior to the query execution.

Here we are going to implement a sample of GraphQL API protecting it by creating claims-based authorization. To know more about GrapQL API Integration In Asp.Net Core Application Click Here.

Identity Server4 Token Based Authentication:

In this sample, we are going to use token-based authentication by IdentityServer 4. If you want you can use any other authentication type like cookie authentication or OAuth2.0 or Microsoft Login Identity. Click here for Identity Server4 Sample Source Code.

Dotnet Core Web API Verify IdentityServer4 Authentication Token:

Let's create a Dotnet Core Web API project, where we are going to configure and protect GraphQL API.
       

Note:- Following steps are related verifying the IdentityServer4 authentication token, you can skip the following configurations if you are using another login types.

Add the following NuGet for Bearer Token verification
   Install-Package Microsoft.AspNetCore.Authentication.JwtBearer -Version 3.1.0

Now configure JwtBearer token services

Startup.cs:(ConfigureServices method)

services.AddAuthentication("Bearer")
.AddJwtBearer("Bearer", options =>
{
 options.Authority = "https://localhost:5001";
 options.Audience = "graphQLApi";
});
Add Authentication middleware service just above Authorization middleware service

Startup.cs:(Configure method)

app.UseAuthentication();

Configure DbContext And Repositories To Access Data:

Let's quickly add DbContext and Repository entities to access the data from the database.

Models/Cake.cs:

public class Cake
{
public int Id { get; set; }
public string Name { get; set; }
public decimal Cost { get; set; }
}
Install EntityFrameworkCore NuGet as below
   Install-Package Microsoft.EntityFrameworkCore -Version 3.1.0

Data/BakeryContext.cs:

using Microsoft.EntityFrameworkCore;
using Test.GraphQL.MyCoreAPI.Models;
namespace Test.GraphQL.MyCoreAPI.Data
{
    public class BakeryContext:DbContext
    {
        public BakeryContext(DbContextOptions<BakeryContext> options) : base(options)
        {
        }
        public DbSet<Cake> Cake { get; set; }
    }
}

Now install EntityFrameworkCore SqlServer
     Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 3.1.0

Register DbContext in Startup services as below

Startup.cs(ConfigureServices method):

services.AddDbContext>BakeryContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("BakeryContext")));

Add repositories as below

Repos/CakeRepository.cs:

public class CakeRepository : ICakeRepository
{
 private readonly BakeryContext _bakeryContext;
 public CakeRepository(BakeryContext bakeryContext)
 {
  _bakeryContext = bakeryContext;
 }

 public List>Cake< GetCakes()
 {
  return _bakeryContext.Cake.ToList();
 }
}

Repos/ICakeRepository.cs:

public interface ICakeRepository
{
 List<Cake> GetCakes();
}

Now register  repositories in startup file as below

Startup.cs(ConfigureServices method):

services.AddScoped<ICakeRepository, CakeRepository>();

GraphQL NuGet:

Install following NuGet to configure GraphQL API
    Install-Package GraphQL -Version 2.4.0

ObjectGraphType OR ObjectGraphType<T>:

ObjectGraphType is one of the main building blocks in GraphQL API. In dotnet, every table will be represented by a class. These POCO classes can't be understood by GraphQL API, so for each and every class in c#, we need to create classes that inherit ObjectGraphType(these will be understood by GraphQL API). The class inherits ObjectGraphType need to register all the fields in its constructor because only registered fields will be served by the GraphQL API.

GraphQLModels/CakeType:

using GraphQL.Types;
using Test.GraphQL.MyCoreAPI.Models;
namespace Test.GraphQL.MyCoreAPI.GraphQLModel
{
    public class CakeType : ObjectGraphType<Cake>
    {
        public CakeType()
        {
            Field(_ => _.Id);
            Field(_ => _.Name);
            Field(_ => _.Cost);
        }
    }
}
Here CakeType inheriting ObjectGraphType<Cake>. CakeType is a GrpahQL API Type of Cake Class. In Constructor, we register all the fields of Cake class into the CakeType class(GraphQL API Type).

GraphQLModels/RootQueryType.cs:

using GraphQL.Types;
using Test.GraphQL.MyCoreAPI.Repos;

namespace Test.GraphQL.MyCoreAPI.GraphQLModel
{
    public class RootQueryType : ObjectGraphType
    {
        public RootQueryType(ICakeRepository cakeRepository)
        {
            Field<ListGraphType<CakeType>>("allCakes", resolve: context =>
             {
                 return cakeRepository.GetCakes();
             });
        }
    }
}
RootQueryType is a parent of all other classes which inherits ObjectGraphType. In this class, we need to register all our select API queries. Every field in this class represents an API select query.

GraphQL API is fully supported with dependency injection, so every class which inherits ObjectGraphType needs to be registered in startup services.

Startup.cs(ConfigureServices method):

services.AddScoped<RootQueryType>();
services.AddScoped<CakeType>();

GraphQL Schema:

GraphQL Schema is an execution point for any select query or mutation query(query to update the data in database)

GraphQLModel/RootSchema:

using GraphQL;
using GraphQL.Types;

namespace Test.GraphQL.MyCoreAPI.GraphQLModel
{
    public class RootSchema : Schema, ISchema
    {
        public RootSchema(IDependencyResolver resolver) : base(resolver)
        {
            Query = resolver.Resolve<RootQueryType>();
        }
    }
}
Now register IDependencyResolver and RootSchema in startup services

Startup.cs(ConfigureServices method):

services.AddScoped<IDependencyResolver>(_ => new FuncDependencyResolver(_.GetRequiredService));
services.AddScoped<ISchema, RootSchema>();

Create An GraphQL EndPoint:

Models/GraphQLQueryDto.cs:

public class GraphQLQueryDto
{
 public string Query { get; set; }
}

Controller/GraphQLController:

using System.Linq;
using System.Threading.Tasks;
using GraphQL;
using GraphQL.Types;
using Microsoft.AspNetCore.Mvc;
using Test.GraphQL.MyCoreAPI.Models;

namespace Test.GraphQL.MyCoreAPI.Controllers
{
    [Route("graphql")]
    public class GraphQLController : Controller
    {
        private readonly ISchema _schema;
        private readonly IDocumentExecuter _executer;
        public GraphQLController(ISchema schema, IDocumentExecuter executer)
        {
            _schema = schema;
            _executer = executer;
        }

        [HttpPost]
        public async Task Post([FromBody] GraphQLQueryDto query)
        {
            var result = await _executer.ExecuteAsync(_ =>
            {
                _.Schema = _schema;
                _.Query = query.Query;
               
            }).ConfigureAwait(false);

            if (result.Errors?.Count > 0)
            {
                return Problem(detail: result.Errors.Select(_ => _.Message).FirstOrDefault(), statusCode: 500);
            }
            return Ok(result.Data);
        }
    }
}

Startup.cs(ConfigureServices):

services.AddSingleton<IDocumentExecuter, DocumentExecuter>();

GraphL Test Query:

query 
{ 
  allCakes
  {
 id 
 name
  } 
}
Now test the API as below
       

Implement IValidationRule To Allow Authenticated User:

Now to write validation rules we need to implement IValidationRule interface as below

Helper/AuthValidationRule:

using System.Security.Claims;
using GraphQL.Validation;

namespace Test.GraphQL.MyCoreAPI.Helper
{
    public class AuthValidationRule : IValidationRule
    {
        public INodeVisitor Validate(ValidationContext context)
        {
            var userContext = context.UserContext as ClaimsPrincipal;
            var authenticated = userContext?.Identity?.IsAuthenticated ?? false;


            return new EnterLeaveListener(_ =>
            {
                if (!authenticated)
                {
                    context.ReportError(new ValidationError(
                        context.OriginalQuery,
                        "authentication-required",
                        "Api can accessed by only autherized user"
                        ));
                }
            });
        }
    }
}
On implementing the IValidationRule interface we need to implement Validate method as above. From ValidationContext we can get ClaimsPrincipal to check user authenticated. If the user not authenticated we can return custom error using the ValidationError entity.

Now register our AuthValidationRule in startup services

Startup.cs(ConfigureServices):

services.AddSingleton<IValidationRule, AuthValidationRule>();
Now we need to pass the validation rules to IDocumentExecuter so that validation rules get executed before any query execution.

Controller/GraphQLController.cs:(Inject IValidationRule)

private readonly IValidationRule _validationRule;

public GraphQLController(
 IValidationRule validationRule)
{
 _validationRule = validationRule;
}

Controller/GraphQLController.cs:(assign IvalidationRule to IDocumentExecuter):

var result = await _executer.ExecuteAsync(_ =>
{
 _.ValidationRules = new List<IValidationRule> { _validationRule };
   
}).ConfigureAwait(false);
Now try to access the endpoint we can see an error like need authentication to access API as below
     
Now request API endpoint by adding Authorization header with IdentityServer4 token as below
   
Now try to access the endpoint, we can see the same error as not authenticated, this because if you recall IValidationRule above we discussed, there we are using 'ValidationContext.UserContex'  which is empty. We need to pass user data to the GraphQL context, we can achieve it bypassing the user data to IDocumentExecuter.

Controller/GraphQLController.cs:(inject httpContext where user context can access):

private readonly IHttpContextAccessor _httpContextAccessor;
public GraphQLController(
 IHttpContextAccessor httpContextAccessor)
{
 _httpContextAccessor = httpContextAccessor;
}

[HttpPost]
public async Task<IActionResult> Post([FromBody] GraphQLQueryDto query)
{
// display purpose existing code hidden
 var result = await _executer.ExecuteAsync(_ =>
 {
  
  _.UserContext = _httpContextAccessor.HttpContext.User;
    
 }).ConfigureAwait(false);

}

Startup.cs:

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
Now if we test API with the access token in authorization header we can see we are able to access GraphQL API endpoint successfully.

Operation Level Authentication:

In GraphQL API using IValidationRule able to setup authentication rules based on "GraphQL.Language.AST.Operation". The two main GraphQL operations like 'Query Operation' represent API data fetching and 'Mutation Operation' represents API posting data.

Now to enable user authentication mandatory while fetching data update validation rule as below

Helper/AuthValidationRule:(authentication while fetching data)

return new EnterLeaveListener(_ =>
{
_.Match<Operation>(op =>
{
 if (op.OperationType == OperationType.Query && !authenticated)
 {
  context.ReportError(new ValidationError(
   context.OriginalQuery,
   "auth-required",
   $"Authorization is required to fetch data",
   op));
 }
});
});
Similarly to enable user authentication while saving data to API change the operation types as 'OperationType.Mutation'.

Claim-based Authorization At Field:

Claim-based authorization at fields in root Query or root Mutation is the best approach in GraphQL.
Now we need to register fields with their respective claims if needed. Let's recall our RootQuery field which is looks as below.
Field<ListGraphType<CakeType>>("allCakes", resolve: context =>
{
return cakeRepository.GetCakes();
});
A field variable is of type 'GraphQL.Types.FieldTypes'. GraphQL.Types.FieldTypes implements IProviderMetaData which looks as below.

IProviderMetaData(GraphQL Library Interface):

namespace GraphQL.Types
{
    public interface IProvideMetadata
    {
        IDictionary<string, object> Metadata { get; }

        TType GetMetadata<TType>(string key, TType defaultValue = default);
        bool HasMetadata(string key);
    }
}
From the above interface MetaData property of the dictionary, will be used to add permission to the fields.

Let's implement an extension method to add claims to the fields in Root Query or Root Mutation.

Extens/PermissionExtention.cs:

public static class PermissionExtenstion
{
 public static readonly string PermissionKey = "permission";
 
 public static void AddPermissions(this IProvideMetadata type, string claim)
 {
  var permissions = type.GetMetadata<List<string>>(PermissionKey);
  if (permissions == null)
  {
   permissions = new List<string>();
  }
  permissions.Add(claim);
  type.Metadata[PermissionKey] = permissions;
 }
}
Here we can see claims string added to Metadata Property of IProvideMetadata. This stored claims will be checked in validation rules in later steps.

Now we need to update the field with its claim so that it will be accessed to the users having that claim.

GraphQLModel/RootQueryType(Update field with claim):

Field<ListGraphType<CakeType>>("allCakes", resolve: context =>
{
 return cakeRepository.GetCakes();
}).AddPermissions("super admin");
Only "super admin" have permission to access this query field.

We have a method to add claims, now we need to write an extension to match the claim as below

Extens/PermissionExtentsion.cs:(add below method)

public static bool HasClaimsMatched(this IProvideMetadata type, IEnumerable<string> claimes)
{
 var permissions = type.GetMetadata<IEnumerable<string>>(PermissionKey, new List<string> { });
 return permissions.Any(x => claimes.Contains(x));
}

Now we need to update validation rules to check matching claim existed as below:

Helper/AuthValidationRule.cs:

public class AuthValidationRule : IValidationRule
{
 public INodeVisitor Validate(ValidationContext context)
 {
  var userContext = context.UserContext as ClaimsPrincipal;
  var authenticated = userContext?.Identity?.IsAuthenticated ?? false;


  return new EnterLeaveListener(_ =>
  {
   _.Match<Field>(fieldAst =>
   {
    var fieldDef = context.TypeInfo.GetFieldDef();
    var claims = userContext.Claims.Select(_ => _.Value).ToList();
    if (
     (!authenticated || !fieldDef.HasClaimsMatched(claims)))
    {
     context.ReportError(new ValidationError(
      context.OriginalQuery,
      "auth-required",
      $"You are not authorized to run this query.",
      fieldAst));
    }
   });
  });
 }
}
Here context.TypeInfo gets the information about the query field type. Here we are checking our login claims with the field registered claims using the extension method HasClaimsMatched.

Now test the API with the access token in the authorization header with appropriate user claims. we are able to access the data from GraphQL endpoint.

If we observe the validation rules has been implemented like only authenticated user with appropriate claims can access the data from GrpahQL endpoint. But in some applications have a combination of accessing data with and without authentication. In those scenarios, our rules will be failed.

So we need to identify our fields have been registered with claims or not. If any field doesn't have claims registered then we can allow the user to access those fields without checking for authentication

Let's implement a new extension method to check whether the field in RootQuery has been registered with any claim as below

Extens/PermissionExtension.cs:

public static bool AnyPermissions(this IProvideMetadata type)
{
 var permissions = type.GetMetadata<IEnumerable<string>>(PermissionKey, new List<string> { });
 return permissions.Any();
}
Now update the validation rules as below:

 Helper/AuthValidationRule.cs:

_.Match<Field>(fieldAst =>
{
 var fieldDef = context.TypeInfo.GetFieldDef();
 var claims = userContext.Claims.Select(_ => _.Value).ToList();
 if (fieldDef.AnyPermissions() &&
  (!authenticated || !fieldDef.HasClaimsMatched(claims)))
 {
  context.ReportError(new ValidationError(
   context.OriginalQuery,
   "auth-required",
   $"You are not authorized to run this query.",
   fieldAst));
 }
});
Here 'fieldDef.AnyPermissions()' check whether the GraphQL field registered with claims or not. Now we can access both query fields with and without user claims.

Wrapping Up:

Hopefully, this article will help to implement GraphQL API authorization in the Dotnet core. I will love to have your feedback, suggestions and better techniques in the comments section.

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