diff --git a/packages/openauth/src/provider/code.ts b/packages/openauth/src/provider/code.ts
index e8f7b709..0dacd72f 100644
--- a/packages/openauth/src/provider/code.ts
+++ b/packages/openauth/src/provider/code.ts
@@ -96,6 +96,37 @@ export interface CodeProviderConfig<
    * ```
    */
   sendCode: (claims: Claims, code: string) => Promise<void | CodeProviderError>
+  /**
+   * Controls whether claims (email, phone, etc.) are allowed to receive codes.
+   *
+   * @default true
+   *
+   * @example
+   * ```ts
+   * // Allow only company emails
+   * {
+   *   allowClaims: (claims) => {
+   *     return claims.email?.endsWith("@company.com") || false
+   *   }
+   * }
+   *
+   * // Only allow existing users
+   * {
+   *   allowClaims: async (claims) => {
+   *     return await externalDB.userExists(claims.email)
+   *   }
+   * }
+   *
+   * // Combined: domain + existence check
+   * {
+   *   allowClaims: async (claims) => {
+   *     return claims.email?.endsWith("@company.com") &&
+   *            await externalDB.userExists(claims.email)
+   *   }
+   * }
+   * ```
+   */
+  allowClaims?: boolean | ((claims: Claims) => boolean | Promise<boolean>)
 }
 
 /**
@@ -124,6 +155,7 @@ export type CodeProviderState =
  * | ----- | ----------- |
  * | `invalid_code` | The code is invalid. |
  * | `invalid_claim` | The _claim_, email or phone number, is invalid. |
+ * | `claims_not_allowed` | The claims are not allowed. |
  */
 export type CodeProviderError =
   | {
@@ -134,6 +166,9 @@ export type CodeProviderError =
       key: string
       value: string
     }
+  | {
+      type: "claims_not_allowed"
+    }
 
 export function CodeProvider<
   Claims extends Record<string, string> = Record<string, string>,
@@ -175,6 +210,22 @@ export function CodeProvider<
         if (action === "request" || action === "resend") {
           const claims = Object.fromEntries(fd) as Claims
           delete claims.action
+
+          // Validate claims are allowed
+          if (config.allowClaims !== undefined) {
+            let allowed = true
+            if (typeof config.allowClaims === "boolean") {
+              allowed = config.allowClaims
+            } else if (typeof config.allowClaims === "function") {
+              allowed = await config.allowClaims(claims)
+            }
+            if (!allowed) {
+              return transition(c, { type: "start" }, fd, {
+                type: "claims_not_allowed",
+              })
+            }
+          }
+
           const err = await config.sendCode(claims, code)
           if (err) return transition(c, { type: "start" }, fd, err)
           return transition(
diff --git a/packages/openauth/src/provider/password.ts b/packages/openauth/src/provider/password.ts
index 850af8a3..2236c5db 100644
--- a/packages/openauth/src/provider/password.ts
+++ b/packages/openauth/src/provider/password.ts
@@ -141,6 +141,47 @@ export interface PasswordConfig {
   validatePassword?:
     | v1.StandardSchema
     | ((password: string) => Promise<string | undefined> | string | undefined)
+  /**
+   * Controls whether new user registration is allowed.
+   *
+   * This allows implementing sign-up restrictions, domain validation,
+   * or completely disable sign-ups.
+   *
+   * @default true
+   *
+   * @example
+   * ```ts
+   * // Disable all registrations
+   * {
+   *   allowRegistration: false
+   * }
+   *
+   * // Allow only specific email domains
+   * {
+   *   allowRegistration: (email) => {
+   *     return email.endsWith("@company.com")
+   *   }
+   * }
+   * ```
+   */
+  allowRegistration?: boolean | ((email: string) => boolean | Promise<boolean>)
+  /**
+   * Callback to check if a user exists in an external system.
+   *
+   * Used when allowRegistration is false to validate existing users
+   * during password reset flow.
+   *
+   * @example
+   * ```ts
+   * {
+   *   userExists: async (email) => {
+   *     // Check your external user database
+   *     return await externalDB.userExists(email)
+   *   }
+   * }
+   * ```
+   */
+  userExists?: (email: string) => boolean | Promise<boolean>
 }
 
 /**
@@ -172,6 +213,7 @@ export type PasswordRegisterState =
  * | `invalid_code` | The code is invalid. |
  * | `invalid_password` | The password is invalid. |
  * | `password_mismatch` | The passwords do not match. |
+ * | `registration_not_allowed` | Registration is not allowed for this email. |
  */
 export type PasswordRegisterError =
   | {
@@ -193,6 +235,9 @@ export type PasswordRegisterError =
       type: "validation_error"
       message?: string
     }
+  | {
+      type: "registration_not_allowed"
+    }
 
 /**
  * The state of the password change flow.
@@ -311,6 +356,9 @@ export function PasswordProvider(
       })
 
       routes.get("/register", async (c) => {
+        if (config.allowRegistration === false) {
+          return c.redirect(getRelativeUrl(c, "./authorize"), 302)
+        }
         const state: PasswordRegisterState = {
           type: "start",
         }
@@ -341,6 +389,20 @@ export function PasswordProvider(
           const password = fd.get("password")?.toString()
           const repeat = fd.get("repeat")?.toString()
           if (!email) return transition(provider, { type: "invalid_email" })
+
+          // Check if registration is allowed for this email
+          if (config.allowRegistration !== undefined) {
+            let allowed = true
+            if (typeof config.allowRegistration === "boolean") {
+              allowed = config.allowRegistration
+            } else if (typeof config.allowRegistration === "function") {
+              allowed = await config.allowRegistration(email)
+            }
+            if (!allowed) {
+              return transition(provider, { type: "registration_not_allowed" })
+            }
+          }
+
           if (!password)
             return transition(provider, { type: "invalid_password" })
           if (password !== repeat)
@@ -481,7 +543,27 @@ export function PasswordProvider(
             provider.email,
             "password",
           ])
-          if (!existing) return c.redirect(provider.redirect, 302)
+
+          // If user doesn't exist in storage, check if they exist in external system
+          // Only do this when registrations are disabled (allowRegistration === false)
+          if (!existing) {
+            if (config.allowRegistration === false && config.userExists) {
+              if (await config.userExists(provider.email)) {
+                // Create user in storage so password can be set
+                await Storage.set(
+                  ctx.storage,
+                  ["email", provider.email, "password"],
+                  Math.random().toString(36), // Temporary placeholder that will be replaced
+                )
+              } else {
+                // User doesn't exist in external system, redirect to login
+                return c.redirect(provider.redirect, 302)
+              }
+            } else {
+              // Registration allowed or no userExists callback, use default behavior (redirect to login)
+              return c.redirect(provider.redirect, 302)
+            }
+          }
 
           const password = fd.get("password")?.toString()
           const repeat = fd.get("repeat")?.toString()
diff --git a/packages/openauth/src/ui/code.tsx b/packages/openauth/src/ui/code.tsx
index 5ed77392..5191024c 100644
--- a/packages/openauth/src/ui/code.tsx
+++ b/packages/openauth/src/ui/code.tsx
@@ -70,12 +70,16 @@ const DEFAULT_COPY = {
    * Copy for the resend button.
    */
   code_resend: "Resend",
+  /**
+   * Error message when claims are not allowed.
+   */
+  error_claims_not_allowed: "Access not allowed.",
 }
 
 export type CodeUICopy = typeof DEFAULT_COPY
 
 /**
- * Configure the password UI.
+ * Configure the code UI.
  */
 export interface CodeUIOptions {
   /**
@@ -101,6 +105,31 @@ export interface CodeUIOptions {
    * @default "email"
    */
   mode?: "email" | "phone"
+  /**
+   * Controls whether claims (email, phone, etc.) are allowed to receive codes.
+   *
+   * @default true
+   *
+   * @example
+   * ```ts
+   * // Allow only company emails
+   * {
+   *   allowClaims: (claims) => {
+   *     return claims.email?.endsWith("@company.com") || false
+   *   }
+   * }
+   *
+   * // Only allow existing users
+   * {
+   *   allowClaims: async (claims) => {
+   *     return await externalDB.userExists(claims.email)
+   *   }
+   * }
+   * ```
+   */
+  allowClaims?:
+    | boolean
+    | ((claims: Record<string, string>) => boolean | Promise<boolean>)
 }
 
 /**
@@ -117,6 +146,7 @@ export function CodeUI(props: CodeUIOptions): CodeProviderOptions {
 
   return {
     sendCode: props.sendCode,
+    allowClaims: props.allowClaims,
     length: 6,
     request: async (_req, state, _form, error): Promise<Response> => {
       if (state.type === "start") {
@@ -126,6 +156,9 @@ export function CodeUI(props: CodeUIOptions): CodeProviderOptions {
               {error?.type === "invalid_claim" && (
                 <FormAlert message={copy.email_invalid} />
               )}
+              {error?.type === "claims_not_allowed" && (
+                <FormAlert message={copy.error_claims_not_allowed} />
+              )}
               <input type="hidden" name="action" value="request" />
               <input
                 data-component="input"
diff --git a/packages/openauth/src/ui/password.tsx b/packages/openauth/src/ui/password.tsx
index 360f28da..b74090b9 100644
--- a/packages/openauth/src/ui/password.tsx
+++ b/packages/openauth/src/ui/password.tsx
@@ -59,6 +59,10 @@ const DEFAULT_COPY = {
    * Error message when the user enters a password that fails validation.
    */
   error_validation_error: "Password does not meet requirements.",
+  /**
+   * Error message when registration is not allowed.
+   */
+  error_registration_not_allowed: "Registration is not allowed.",
   /**
    * Title of the register page.
    */
@@ -128,6 +132,14 @@ const DEFAULT_COPY = {
    * Copy for the continue button.
    */
   button_continue: "Continue",
+  /**
+   * Copy for the first-time login message.
+   */
+  first_time_prompt: "First time logging in?",
+  /**
+   * Copy for the reset password link for first-time users.
+   */
+  first_time_reset: "Reset your password",
 } satisfies {
   [key in `error_${
     | PasswordLoginError["type"]
@@ -141,7 +153,10 @@ type PasswordUICopy = typeof DEFAULT_COPY
  * Configure the password UI.
  */
 export interface PasswordUIOptions
-  extends Pick<PasswordConfig, "sendCode" | "validatePassword"> {
+  extends Pick<
+    PasswordConfig,
+    "sendCode" | "validatePassword" | "allowRegistration" | "userExists"
+  > {
   /**
    * Custom copy for the UI.
    */
@@ -160,6 +175,8 @@ export function PasswordUI(input: PasswordUIOptions): PasswordConfig {
   return {
     validatePassword: input.validatePassword,
     sendCode: input.sendCode,
+    allowRegistration: input.allowRegistration,
+    userExists: input.userExists,
     login: async (_req, form, error): Promise<Response> => {
       const jsx = (
         <Layout>
@@ -185,16 +202,28 @@ export function PasswordUI(input: PasswordUIOptions): PasswordConfig {
             />
             <button data-component="button">{copy.button_continue}</button>
             <div data-component="form-footer">
-              <span>
-                {copy.register_prompt}{" "}
-                <a data-component="link" href="register">
-                  {copy.register}
-                </a>
-              </span>
+              {input.allowRegistration !== false && (
+                <span>
+                  {copy.register_prompt}{" "}
+                  <a data-component="link" href="register">
+                    {copy.register}
+                  </a>
+                </span>
+              )}
               <a data-component="link" href="change">
                 {copy.change_prompt}
               </a>
             </div>
+            {input.allowRegistration === false && input.userExists && (
+              <div data-component="form-footer">
+                <span>
+                  {copy.first_time_prompt}{" "}
+                  <a data-component="link" href="change">
+                    {copy.first_time_reset}
+                  </a>
+                </span>
+              </div>
+            )}
           </form>
         </Layout>
       )