IdentityServer4 實現自定義 GrantType 授權模式

OAuth 2.0 預設四種授權模式（GrantType）：

• 授權碼模式（authorization_code）
• 簡化模式（implicit）
• 密碼模式（password）
• 客戶端模式（client_credentials）

使用 IdentityServer4，我們可以自定義授權模式嗎？答案是可以的，比如我們自定義實現一個anonymous授權模式（匿名訪問）。

創建AnonymousGrantValidator（繼承IExtensionGrantValidator）：

public class AnonymousGrantValidator : IExtensionGrantValidator
{
    private readonly ITokenValidator _validator;

    public AnonymousGrantValidator(ITokenValidator validator)
    {
        _validator = validator;
    }

    public string GrantType => "anonymous";

    public async Task ValidateAsync(ExtensionGrantValidationContext context)
    {
        //var userToken = context.Request.Raw.Get("token");

        //if (string.IsNullOrEmpty(userToken))
        //{
        //    context.Result = new GrantValidationResult(TokenRequestErrors.InvalidGrant);
        //    return;
        //}

        //var result = await _validator.ValidateAccessTokenAsync(userToken);
        //if (result.IsError)
        //{
        //    context.Result = new GrantValidationResult(TokenRequestErrors.InvalidGrant);
        //    return;
        //}

        // get user's identity
        //var sub = result.Claims.FirstOrDefault(c => c.Type == "sub").Value;

        var claims = new List<Claim>() { new Claim("role", GrantType) }; // Claim 用於配置服務站點 [Authorize("anonymous")]
        context.Result = new GrantValidationResult(GrantType, GrantType, claims);
    }
}

修改Client配置：

new Client
{
    ClientId = "client1",
    AllowedGrantTypes = GrantTypes.List(GrantTypes.ResourceOwnerPassword.FirstOrDefault(), "anonymous"), //一個 Client 可以配置多個 GrantType
    AllowOfflineAccess = true,
    AccessTokenLifetime = 3600 * 6, //6小時
    SlidingRefreshTokenLifetime = 1296000, //15天
    ClientSecrets =
    {
        new Secret("123".Sha256())
    },
    AllowedScopes = new List<string>
    {
        "api2"
    }
}

DI 增加註入對象：

builder.AddExtensionGrantValidator<AnonymousGrantValidator>();

調用示例代碼：

public async Task<TokenResponse> AnonymousAsync(string userToken)
{
    var payload = new
    {
        token = userToken
    };

    // create token client
    var client = new TokenClient(disco.TokenEndpoint, "client1", "123");

    // send custom grant to token endpoint, return response
    return await client.RequestCustomGrantAsync("anonymous", "api2", payload);
}

Http 訪問示例：

POST /connect/token

grant_type=anonymous&
scope=api2&
token=...&
client_id=api1.client
client_secret=secret

參考資料：

• Extension Grants