Initial implementation.

.gitignore

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+.dub
+docs.json
+__dummy.html
+docs/
+/jwt4d
+jwt4d.so
+jwt4d.dylib
+jwt4d.dll
+jwt4d.a
+jwt4d.lib
+jwt4d-test-*
+*.exe
+*.pdb
+*.o
+*.obj
+*.lst
+*.a

dub.json

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+{
+	"authors": [
+		"Andrew Lalis"
+	],
+	"copyright": "Copyright © 2025, Andrew Lalis",
+	"dependencies": {
+		"secured": "~>3.0.0"
+	},
+	"description": "JSON Web Token library to generate, parse, sign, and verify JWTs.",
+	"license": "CC0",
+	"name": "jwt4d",
+	"targetType": "library"
+}

dub.selections.json

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+{
+	"fileVersion": 1,
+	"versions": {
+		"openssl": "3.3.4",
+		"secured": "3.0.0"
+	}
+}

source/jwt4d/model.d

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+module jwt4d.model;
+
+import std.json;
+import std.typecons : Nullable;
+import std.base64;
+import secured;
+
+/**
+ * Enum defining the names of registered JWT claims, as per RFC 7519.
+ */
+enum JwtClaim {
+    Issuer = "iss",
+    Subject = "sub",
+    Audience = "aud",
+    Expiration = "exp",
+    NotBefore = "nbf",
+    IssuedAt = "iat",
+    JwtId = "jti"
+}
+
+/**
+ * Data structure containing a JWT's claims.
+ */
+struct JwtClaims {
+    private JSONValue obj = JSONValue.emptyObject;
+    
+    ref issuer(string issuer) {
+        if (issuer is null) {
+            this.obj.object.remove(JwtClaim.Issuer);
+        } else {
+            this.obj.object[JwtClaim.Issuer] = issuer;
+        }
+        return this;
+    }
+
+    string issuer() const {
+        if (JwtClaim.IssuedAt !in this.obj.object) return null;
+        return this.obj.object[JwtClaim.Issuer].str;
+    }
+
+    ref subject(string subject) {
+        if (subject is null) {
+            this.obj.object.remove(JwtClaim.Subject);
+        } else {
+            this.obj.object[JwtClaim.Subject] = subject;
+        }
+        return this;
+    }
+
+    string subject() const {
+        if (JwtClaim.Subject !in this.obj.object) return null;
+        return this.obj.object[JwtClaim.Subject].str;
+    }
+
+    ref audience(string audience) {
+        if (audience is null) {
+            this.obj.object.remove(JwtClaim.Audience);
+        } else {
+            this.obj.object[JwtClaim.Audience] = audience;
+        }
+        return this;
+    }
+
+    ref audience(string[] audiences) {
+        if (audiences is null || audiences.length == 0) {
+            this.obj.object.remove(JwtClaim.Audience);
+        } else {
+            this.obj.object[JwtClaim.Audience] = audiences;
+        }
+        return this;
+    }
+
+    string audience() const {
+        if (
+            JwtClaim.Audience !in this.obj.object ||
+            this.obj.object[JwtClaim.Audience].type != JSONType.STRING
+        ) return null;
+        return this.obj.object[JwtClaim.Audience].str;
+    }
+
+    string[] audiences() const {
+        import std.algorithm : map;
+        import std.array : array;
+        if (
+            JwtClaim.Audience !in this.obj.object ||
+            this.obj.object[JwtClaim.Audience].type != JSONType.ARRAY
+        ) return [];
+        return this.obj.object[JwtClaim.Audience].array.map!(v => v.str).array;
+    }
+
+    ref expiration(long expiration) {
+        if (expiration < 0) {
+            this.obj.object.remove(JwtClaim.Expiration);
+        } else {
+            this.obj.object[JwtClaim.Expiration] = expiration;
+        }
+        return this;
+    }
+
+    ref notBefore(long notBefore) {
+        if (notBefore < 0) {
+            this.obj.object.remove(JwtClaim.NotBefore);
+        } else {
+            this.obj.object[JwtClaim.NotBefore] = notBefore;
+        }
+        return this;
+    }
+
+    ref issuedAt(long issuedAt) {
+        if (issuedAt < 0) {
+            this.obj.object.remove(JwtClaim.IssuedAt);
+        } else {
+            this.obj.object[JwtClaim.IssuedAt] = issuedAt;
+        }
+        return this;
+    }
+
+    ref jwtId(string jwtId) {
+        if (jwtId is null) {
+            this.obj.object.remove(JwtClaim.JwtId);
+        } else {
+            this.obj.object[JwtClaim.JwtId] = jwtId;
+        }
+        return this;
+    }
+
+    string toJson() const {
+        return this.obj.toJSON();
+    }
+}
+
+string writeJwt(in JwtClaims claims, string secret) {
+    JSONValue headerObj = JSONValue.emptyObject;
+    headerObj.object["typ"] = "JWT";
+    headerObj.object["alg"] = "HS256";
+    string headerBase64 = Base64URLNoPadding.encode(cast(ubyte[]) headerObj.toJSON());
+
+    string claimsBase64 = Base64URLNoPadding.encode(cast(ubyte[]) claims.toJson());
+
+    string prefix = headerBase64 ~ "." ~ claimsBase64;
+
+    ubyte[] signatureBytes = hmac_ex(
+        cast(ubyte[]) secret,
+        cast(ubyte[]) (prefix),
+        HashAlgorithm.SHA2_256
+    );
+    string signatureBase64 = Base64URLNoPadding.encode(signatureBytes);
+
+    return prefix ~ "." ~ signatureBase64;
+}
+
+unittest {
+    JwtClaims claims;
+    claims.issuer = "example.com";
+    claims.subject = "user123";
+    claims.expiration = 123;
+
+    string token = writeJwt(claims, "test");
+    import std.stdio;
+    writeln(token);
+}
+
+JwtClaims readJwt(string token, string secret) {
+    import std.algorithm : splitter;
+    import std.array : array;
+
+    auto parts = token.splitter('.').array;
+    JSONValue headerObj = parseJSON(cast(string) Base64URLNoPadding.decode(parts[0]));
+    // TODO: Verify header object and algorithm.
+    JSONValue claimsObj = parseJSON(cast(string) Base64URLNoPadding.decode(parts[1]));
+    // TODO: Verify claims object structure.
+    ubyte[] signatureBytes = Base64URLNoPadding.decode(parts[2]);
+    bool verified = hmac_verify_ex(
+        signatureBytes,
+        cast(ubyte[]) secret,
+        cast(ubyte[]) (parts[0] ~ "." ~ parts[1]),
+        HashAlgorithm.SHA2_256
+    );
+    if (!verified) {
+        throw new Exception("Verification failed!");
+        // TODO: Custom error handling.
+    }
+    return JwtClaims(claimsObj);
+}
+
+unittest {
+    JwtClaims claims;
+    claims.issuer = "example.com";
+    string token = writeJwt(claims, "test");
+    JwtClaims readClaims = readJwt(token, "test");
+    import std.stdio;
+    writeln(readClaims.toJson());
+}

source/jwt4d/package.d

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+module jwt4d;
+