1 files changed, 25 insertions, 0 deletions
diff --git a/src/FundLab.Api/Authentication.fs b/src/FundLab.Api/Authentication.fs
new file mode 100644
index 0000000..e98d71e
--- /dev/null
+++ b/src/FundLab.Api/Authentication.fs
@@ -0,0 +1,25 @@
+namespace FundLab.Api
+
+open System
+open System.Security.Cryptography
+open System.Text
+
+type AuthDecision =
+    | Authorized
+    | Unauthorized
+
+module Authentication =
+    let authorize (expectedToken: string) (authorizationHeader: string) : AuthDecision =
+        if String.IsNullOrWhiteSpace expectedToken
+           || String.IsNullOrWhiteSpace authorizationHeader
+           || not (authorizationHeader.StartsWith("Bearer ", StringComparison.OrdinalIgnoreCase)) then
+            AuthDecision.Unauthorized
+        else
+            let presentedToken = authorizationHeader.Substring("Bearer ".Length)
+            let expectedBytes = Encoding.UTF8.GetBytes expectedToken
+            let presentedBytes = Encoding.UTF8.GetBytes presentedToken
+
+            if CryptographicOperations.FixedTimeEquals(expectedBytes, presentedBytes) then
+                AuthDecision.Authorized
+            else
+                AuthDecision.Unauthorized