--- title: From API key to user with ASP.NET Web API | daily.dev description: A tutorial shows how to authenticate API consumers in ASP.NET Web API using a custom X-ApiKey HTTP header instead of forms, Windows, or basic authentication.... canonical: https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: From API key to user with ASP.NET Web API | daily.dev og:description: A tutorial shows how to authenticate API consumers in ASP.NET Web API using a custom X-ApiKey HTTP header instead of forms, Windows, or basic authentication.... og:url: https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5 og:image: https://api.daily.dev/og/posts/P3UgtmPF5.png og:image:alt: From API key to user with ASP.NET Web API og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # From API key to user with ASP.NET Web API **[Maarten Balliauw](https://daily.dev/sources/maartenballiauw)** · 4 min read · 0 upvotes · 0 comments ## Summary A tutorial shows how to authenticate API consumers in ASP.NET Web API using a custom X-ApiKey HTTP header instead of forms, Windows, or basic authentication. It walks through building a DelegatingHandler called AuthorizationHeaderHandler that reads the header, maps it to a ClaimsIdentity and ClaimsPrincipal, and assigns it to the current thread so the standard [Authorize] attribute and User property work as expected. The approach is noted as adaptable to OAuth2 tokens as well. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I authenticate API requests using a custom API key header in ASP.NET Web API? Create a DelegatingHandler that reads the custom header (for example X-ApiKey) from the incoming HttpRequestMessage, validates it, builds a ClaimsIdentity with the resolved username, wraps it in a ClaimsPrincipal, and assigns it to Thread.CurrentPrincipal. Register the handler with GlobalConfiguration.Configuration.MessageHandlers.Add so it runs on every request, letting [Authorize] and User.Identity.Name work normally. _daily.dev surfaces practical ASP.NET Web API security patterns for developers wiring up custom authentication._ ### Can a DelegatingHandler-based authentication approach in ASP.NET Web API be reused for OAuth2 tokens? Yes, the same DelegatingHandler pattern used for a custom API key header can be adapted for OAuth2 tokens, since OAuth2 ultimately relies on a custom Authorization header at the HTTP level. A similar technique was applied for OAuth2 delegation with Windows Azure Access Control Service, handling OAuth2 tokens the same way the API key is translated into a ClaimsPrincipal. _Developers choosing between API keys and OAuth2 can find implementation patterns like this on daily.dev._ ## Similar posts on daily.dev - [Api Key Authentication in ASP.NET Core](https://daily.dev/posts/api-key-authentication-in-asp-net-core-5jr6dwwxq) · We Are .NET · 3 upvotes · 0 comments - [Role-Based Authorization in ASP.NET Core](https://daily.dev/posts/role-based-authorization-in-asp-net-core-qirbihaku) · C\# Corner · 7 upvotes · 0 comments - [ASP.NET Core Security Explained: Modern Authentication, Authorization, and JWT](https://daily.dev/posts/asp-net-core-security-explained-modern-authentication-authorization-and-jwt-bgq4u3gn4) · Syncfusion · 4 upvotes · 0 comments - [How to implement HMAC authentication in ASP.NET Core](https://daily.dev/posts/how-to-implement-hmac-authentication-in-asp-net-core-awauatewf) · InfoWorld · 1 upvotes · 0 comments - [Claims-Based Authorization in ASP.NET Core](https://daily.dev/posts/claims-based-authorization-in-asp-net-core-mdwlbrcwo) · Code with Mukesh · 6 upvotes · 0 comments --- Tags: [#authentication](https://daily.dev/tags/authentication), [#c#](https://daily.dev/tags/c#) [View this post on daily.dev](https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"From API key to user with ASP.NET Web API","url":"https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5"},"datePublished":"2026-10-04T13:04:40.778Z","dateModified":"2026-10-04T13:08:07.751Z","description":"A tutorial shows how to authenticate API consumers in ASP.NET Web API using a custom X-ApiKey HTTP header instead of forms, Windows, or basic authentication....","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/085578f1fde5cd4b6400cf49287277c4?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/085578f1fde5cd4b6400cf49287277c4?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Maarten Balliauw","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Maarten Balliauw","logo":"https://media.daily.dev/image/upload/s--rOTg3VYO--/f_auto,q_auto/v1791119043/logos/maartenballiauw?_a=BAMAMicg0","url":"https://daily.dev/sources/maartenballiauw"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"authentication,c#","timeRequired":"PT4M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Maarten Balliauw","item":"https://daily.dev/sources/maartenballiauw"},{"@type":"ListItem","position":3,"name":"From API key to user with ASP.NET Web API"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/from-api-key-to-user-with-asp-net-web-api-p3ugtmpf5#faq","mainEntity":[{"@type":"Question","name":"How do I authenticate API requests using a custom API key header in ASP.NET Web API?","acceptedAnswer":{"@type":"Answer","text":"Create a DelegatingHandler that reads the custom header (for example X-ApiKey) from the incoming HttpRequestMessage, validates it, builds a ClaimsIdentity with the resolved username, wraps it in a ClaimsPrincipal, and assigns it to Thread.CurrentPrincipal. 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