fix: incorrect initialization of remaining value within API key (#3648)

* Fixes #3640 - Resolves issue related to incorrect initialization of remaining value within API key.

* Adding test cases for fix of #3640.

* chore: update changeset

---------

Co-authored-by: Bereket Engida <86073083+Bekacru@users.noreply.github.com>

.changeset/salty-banks-heal.md

@@ -0,0 +1,5 @@
+---
+"better-auth": patch
+---
+
+fix(api key): key creation bug where remaining was incorrectly defaulting to a capped value instead of allowing null

packages/better-auth/src/plugins/api-key/api-key.test.ts

@@ -600,6 +600,72 @@ describe("api-key", async () => {
 		expect(apiKey.remaining).toEqual(remaining);
 	});
 
+	it("should create API Key with remaining explicitly set to null", async () => {
+		const apiKey = await auth.api.createApiKey({
+			body: {
+				remaining: null,
+				userId: user.id,
+			},
+		});
+
+		expect(apiKey).not.toBeNull();
+		expect(apiKey.remaining).toBeNull();
+	});
+
+	it("should create API Key with remaining explicitly set to null and refillAmount and refillInterval are also set", async () => {
+		const refillAmount = 10; // Arbitrary non-null value
+		const refillInterval = 1000;
+		const apiKey = await auth.api.createApiKey({
+			body: {
+				remaining: null,
+				refillAmount: refillAmount,
+				refillInterval: refillInterval,
+				userId: user.id,
+			},
+		});
+
+		expect(apiKey).not.toBeNull();
+		expect(apiKey.remaining).toBeNull();
+		expect(apiKey.refillAmount).toBe(refillAmount);
+		expect(apiKey.refillInterval).toBe(refillInterval);
+	});
+
+	it("should create API Key with remaining explicitly set to 0 and refillAmount also set", async () => {
+		const remaining = 0;
+		const refillAmount = 10; // Arbitrary non-null value
+		const refillInterval = 1000;
+		const apiKey = await auth.api.createApiKey({
+			body: {
+				remaining: remaining,
+				refillAmount: refillAmount,
+				refillInterval: refillInterval,
+				userId: user.id,
+			},
+		});
+
+		expect(apiKey).not.toBeNull();
+		expect(apiKey.remaining).toBe(remaining);
+		expect(apiKey.refillAmount).toBe(refillAmount);
+		expect(apiKey.refillInterval).toBe(refillInterval);
+	});
+
+	it("should create API Key with remaining undefined and default value of null is respected with refillAmount and refillInterval provided", async () => {
+		const refillAmount = 10; // Arbitrary non-null value
+		const refillInterval = 1000;
+		const apiKey = await auth.api.createApiKey({
+			body: {
+				refillAmount: refillAmount,
+				refillInterval: refillInterval,
+				userId: user.id,
+			},
+		});
+
+		expect(apiKey).not.toBeNull();
+		expect(apiKey.remaining).toBeNull();
+		expect(apiKey.refillAmount).toBe(refillAmount);
+		expect(apiKey.refillInterval).toBe(refillInterval);
+	});
+
 	it("should create API key with invalid metadata", async () => {
 		let result: { data: ApiKey | null; error: Err | null } = {
 			data: null,

packages/better-auth/src/plugins/api-key/routes/create-api-key.ts

@@ -419,7 +419,8 @@ export function createApiKey({
 				rateLimitMax: rateLimitMax ?? opts.rateLimit.maxRequests ?? null,
 				rateLimitTimeWindow:
 					rateLimitTimeWindow ?? opts.rateLimit.timeWindow ?? null,
-				remaining: remaining || refillAmount || null,
+				remaining:
+					remaining === null ? remaining : remaining ?? refillAmount ?? null,
 				refillAmount: refillAmount ?? null,
 				refillInterval: refillInterval ?? null,
 				rateLimitEnabled: