fix(auth): restore BetterAuth OIDC flow across api/web/compose

apps/api/src/auth/auth.config.ts

@@ -14,6 +14,41 @@ const REQUIRED_OIDC_ENV_VARS = [
   "OIDC_REDIRECT_URI",
 ] as const;
 
+/**
+ * Resolve BetterAuth base URL from explicit auth URL or API URL.
+ * BetterAuth uses this to generate absolute callback/error URLs.
+ */
+export function getBetterAuthBaseUrl(): string | undefined {
+  const configured = process.env.BETTER_AUTH_URL ?? process.env.NEXT_PUBLIC_API_URL;
+
+  if (!configured || configured.trim() === "") {
+    if (process.env.NODE_ENV === "production") {
+      throw new Error(
+        "Missing BetterAuth base URL in production. Set BETTER_AUTH_URL (preferred) or NEXT_PUBLIC_API_URL."
+      );
+    }
+    return undefined;
+  }
+
+  let parsed: URL;
+  try {
+    parsed = new URL(configured);
+  } catch (urlError: unknown) {
+    const detail = urlError instanceof Error ? urlError.message : String(urlError);
+    throw new Error(
+      `BetterAuth base URL must be a valid URL. Current value: "${configured}". Parse error: ${detail}.`
+    );
+  }
+
+  if (process.env.NODE_ENV === "production" && parsed.protocol !== "https:") {
+    throw new Error(
+      `BetterAuth base URL must use https in production. Current value: "${configured}".`
+    );
+  }
+
+  return parsed.origin;
+}
+
 /**
  * Check if OIDC authentication is enabled via environment variable
  */
@@ -59,17 +94,17 @@ export function validateOidcConfig(): void {
     );
   }
 
-  // Additional validation: OIDC_REDIRECT_URI must be a valid URL with /auth/callback path
+  // Additional validation: OIDC_REDIRECT_URI must be a valid URL with /auth/oauth2/callback path
   validateRedirectUri();
 }
 
 /**
  * Validates the OIDC_REDIRECT_URI environment variable.
  * - Must be a parseable URL
- * - Path must start with /auth/callback
+ * - Path must start with /auth/oauth2/callback
  * - Warns (but does not throw) if using localhost in production
  *
- * @throws Error if URL is invalid or path does not start with /auth/callback
+ * @throws Error if URL is invalid or path does not start with /auth/oauth2/callback
  */
 function validateRedirectUri(): void {
   const redirectUri = process.env.OIDC_REDIRECT_URI;
@@ -86,14 +121,14 @@ function validateRedirectUri(): void {
     throw new Error(
       `OIDC_REDIRECT_URI must be a valid URL. Current value: "${redirectUri}". ` +
         `Parse error: ${detail}. ` +
-        `Example: "https://app.example.com/auth/callback/authentik".`
+        `Example: "https://api.example.com/auth/oauth2/callback/authentik".`
     );
   }
 
-  if (!parsed.pathname.startsWith("/auth/callback")) {
+  if (!parsed.pathname.startsWith("/auth/oauth2/callback")) {
     throw new Error(
-      `OIDC_REDIRECT_URI path must start with "/auth/callback". Current path: "${parsed.pathname}". ` +
-        `Example: "https://app.example.com/auth/callback/authentik".`
+      `OIDC_REDIRECT_URI path must start with "/auth/oauth2/callback". Current path: "${parsed.pathname}". ` +
+        `Example: "https://api.example.com/auth/oauth2/callback/authentik".`
     );
   }
 
@@ -120,6 +155,7 @@ function getOidcPlugins(): ReturnType<typeof genericOAuth>[] {
   const clientId = process.env.OIDC_CLIENT_ID;
   const clientSecret = process.env.OIDC_CLIENT_SECRET;
   const issuer = process.env.OIDC_ISSUER;
+  const redirectUri = process.env.OIDC_REDIRECT_URI;
 
   if (!clientId) {
     throw new Error("OIDC_CLIENT_ID is required when OIDC is enabled but was not set.");
@@ -130,6 +166,9 @@ function getOidcPlugins(): ReturnType<typeof genericOAuth>[] {
   if (!issuer) {
     throw new Error("OIDC_ISSUER is required when OIDC is enabled but was not set.");
   }
+  if (!redirectUri) {
+    throw new Error("OIDC_REDIRECT_URI is required when OIDC is enabled but was not set.");
+  }
 
   return [
     genericOAuth({
@@ -139,6 +178,7 @@ function getOidcPlugins(): ReturnType<typeof genericOAuth>[] {
           clientId,
           clientSecret,
           discoveryUrl: `${issuer}.well-known/openid-configuration`,
+          redirectURI: redirectUri,
           pkce: true,
           scopes: ["openid", "profile", "email"],
         },
@@ -203,7 +243,10 @@ export function createAuth(prisma: PrismaClient) {
   // Validate OIDC configuration at startup - fail fast if misconfigured
   validateOidcConfig();
 
+  const baseURL = getBetterAuthBaseUrl();
+
   return betterAuth({
+    baseURL,
     basePath: "/auth",
     database: prismaAdapter(prisma, {
       provider: "postgresql",