This documents all authentication flows in Backstory. Here are the key flows explained:

# 🔐 Core Authentication Flows
1. Registration & Email Verification

    `Registration → Email Sent → Email Verification → Account Activation → Login`
    
    Includes resend verification with rate limiting
    
    Handles expired tokens and error cases

2. Login on Trusted Device

    `Login → Credentials Check → Device Trust Check → Immediate Access`
    
    Fastest path with access/refresh tokens issued immediately

3. Login on New Device (MFA)

    `Login → Credentials Check → New Device Detected → Auto-send MFA Email → MFA Dialog → Code Verification → Access Granted`

    Optional device trust for future logins

4. App Initialization & Token Management

    `App Start → Check Tokens → Auto-refresh if needed → Load Dashboard`

    Handles expired tokens gracefully

# 🛡️ Security Features Covered

## Rate Limiting & Protection

* Login attempt limiting
* MFA resend limiting (max 3)
* Verification email rate limiting
* Account lockout for abuse

## Token Management

* Access token expiration handling
* Refresh token rotation
* Token blacklisting on logout
* Force logout on revoked tokens

## Device Security

* Device fingerprinting
* Trusted device management
* MFA for new devices
* Device removal capabilities

# 🔄 Key Decision Points

1. Has Valid Tokens? → Dashboard vs Login
2. Trusted Device? → Immediate access vs MFA
3. Account Active? → Login vs Error message
4. MFA Code Valid? → Success vs Retry/Lock
5. Token Expired? → Refresh vs Re-login

# 📱 User Experience Flows

## Happy Path (Returning User)
`App Start → Valid Tokens → Dashboard (2 steps)`

## New User Journey
`Registration → Email Verification → Login → Dashboard (4 steps)`

## New Device Login
`Login → MFA Email → Code Entry → Dashboard (3 steps)`

## 🔧 Implementation Notes

**Background Tasks**: Email sending doesn't block user flow

**Error Recovery**: Clear paths back to working states

**Admin Features**: User management and security monitoring

**Future Features**: Password reset flow is mapped out

# Flow Diagram

This diagram serves as the complete authentication architecture reference, showing every possible user journey and system state transition.

```
flowchart TD
    %% ================================
    %% REGISTRATION FLOWS
    %% ================================
    
    Start([User Visits App]) --> CheckTokens{Has Valid Tokens?}
    CheckTokens -->|Yes| LoadUser[Load User Profile]
    CheckTokens -->|No| LandingPage[Landing Page]
    
    LandingPage --> RegisterChoice{Registration Type}
    RegisterChoice --> CandidateReg[Candidate Registration Form]
    RegisterChoice --> EmployerReg[Employer Registration Form]
    RegisterChoice --> LoginPage[Login Page]
    
    %% Candidate Registration Flow
    CandidateReg --> CandidateValidation{Form Valid?}
    CandidateValidation -->|No| CandidateReg
    CandidateValidation -->|Yes| CandidateSubmit[POST /candidates]
    CandidateSubmit --> CandidateCheck{User Exists?}
    CandidateCheck -->|Yes| CandidateError[Show Error: User Exists]
    CandidateError --> CandidateReg
    CandidateCheck -->|No| CandidateEmailSent[Auto-send Verification Email]
    CandidateEmailSent --> CandidateSuccess[Show Success Dialog]
    
    %% Employer Registration Flow  
    EmployerReg --> EmployerValidation{Form Valid?}
    EmployerValidation -->|No| EmployerReg
    EmployerValidation -->|Yes| EmployerSubmit[POST /employers]
    EmployerSubmit --> EmployerCheck{User Exists?}
    EmployerCheck -->|Yes| EmployerError[Show Error: User Exists]
    EmployerError --> EmployerReg
    EmployerCheck -->|No| EmployerEmailSent[Auto-send Verification Email]
    EmployerEmailSent --> EmployerSuccess[Show Success Dialog]
    
    %% Email Verification Flow
    CandidateSuccess --> CheckEmail[User Checks Email]
    EmployerSuccess --> CheckEmail
    CheckEmail --> ClickLink[Click Verification Link]
    ClickLink --> VerifyEmail[GET /verify-email?token=xxx]
    VerifyEmail --> TokenValid{Token Valid & Not Expired?}
    TokenValid -->|No| VerifyError[Show Error: Invalid/Expired Token]
    TokenValid -->|Yes| ActivateAccount[Activate Account in DB]
    ActivateAccount --> VerifySuccess[Show Success: Account Activated]
    VerifySuccess --> RedirectLogin[Redirect to Login]
    
    %% Resend Verification
    VerifyError --> ResendOption{Resend Verification?}
    ResendOption -->|Yes| ResendEmail[POST /auth/resend-verification]
    ResendEmail --> RateLimitCheck{Within Rate Limits?}
    RateLimitCheck -->|No| ResendError[Show Rate Limit Error]
    RateLimitCheck -->|Yes| FindPending{Pending Verification Found?}
    FindPending -->|No| ResendGeneric[Generic Success Message]
    FindPending -->|Yes| ResendSuccess[New Email Sent]
    ResendSuccess --> CheckEmail
    ResendGeneric --> CheckEmail
    ResendOption -->|No| RegisterChoice
    
    %% ================================
    %% LOGIN FLOWS
    %% ================================
    
    RedirectLogin --> LoginPage
    LoginPage --> LoginForm[Enter Email/Password]
    LoginForm --> LoginSubmit[POST /auth/login]
    LoginSubmit --> CredentialsValid{Credentials Valid?}
    CredentialsValid -->|No| LoginError[Show Login Error]
    LoginError --> LoginForm
    
    CredentialsValid -->|Yes| AccountActive{Account Active?}
    AccountActive -->|No| AccountError[Show Account Status Error]
    AccountError --> LoginForm
    
    AccountActive -->|Yes| DeviceCheck{Trusted Device?}
    
    %% Trusted Device Flow
    DeviceCheck -->|Yes| TrustedLogin[Update Last Login]
    TrustedLogin --> IssueTokens[Issue Access + Refresh Tokens]
    IssueTokens --> LoginSuccess[Store Tokens Locally]
    LoginSuccess --> LoadUser
    
    %% New Device Flow (MFA Required)
    DeviceCheck -->|No| NewDevice[Detect New Device]
    NewDevice --> GenerateMFA[Generate 6-digit MFA Code]
    GenerateMFA --> SendMFAEmail[Auto-send MFA Email]
    SendMFAEmail --> MFAResponse[Return MFA Required Response]
    MFAResponse --> ShowMFADialog[Show MFA Input Dialog]
    
    ShowMFADialog --> MFAInput[User Enters 6-digit Code]
    MFAInput --> MFASubmit[POST /auth/mfa/verify]
    MFASubmit --> MFAValid{Code Valid & Not Expired?}
    MFAValid -->|No| MFAError[Show MFA Error]
    MFAError --> MFARetry{Attempts < 5?}
    MFARetry -->|Yes| MFAInput
    MFARetry -->|No| MFALocked[Lock MFA Session]
    MFALocked --> LoginForm
    
    MFAValid -->|Yes| RememberDevice{Remember Device?}
    RememberDevice -->|Yes| AddTrustedDevice[Add to Trusted Devices]
    RememberDevice -->|No| SkipTrust[Skip Adding Device]
    AddTrustedDevice --> MFASuccess[Update Last Login]
    SkipTrust --> MFASuccess
    MFASuccess --> IssueTokens
    
    %% MFA Resend Flow
    ShowMFADialog --> MFAResend{Need Resend?}
    MFAResend -->|Yes| ResendMFA[POST /auth/mfa/resend]
    ResendMFA --> ResendLimit{< 3 Resends?}
    ResendLimit -->|No| ResendLocked[Max Resends Reached]
    ResendLocked --> LoginForm
    ResendLimit -->|Yes| NewMFACode[Generate New Code]
    NewMFACode --> SendNewMFA[Send New Email]
    SendNewMFA --> ShowMFADialog
    
    %% ================================
    %% APP INITIALIZATION & TOKEN MANAGEMENT
    %% ================================
    
    LoadUser --> TokenExpired{Access Token Expired?}
    TokenExpired -->|No| Dashboard[Load Dashboard]
    TokenExpired -->|Yes| RefreshCheck{Has Refresh Token?}
    
    RefreshCheck -->|No| ClearTokens[Clear Local Storage]
    ClearTokens --> LandingPage
    
    RefreshCheck -->|Yes| RefreshAttempt[POST /auth/refresh]
    RefreshAttempt --> RefreshValid{Refresh Token Valid?}
    RefreshValid -->|No| ClearTokens
    RefreshValid -->|Yes| NewTokens[Issue New Access Token]
    NewTokens --> UpdateStorage[Update Local Storage]
    UpdateStorage --> Dashboard
    
    %% ================================
    %% LOGOUT FLOWS
    %% ================================
    
    Dashboard --> LogoutChoice{Logout Type}
    LogoutChoice --> SingleLogout[Logout This Device]
    LogoutChoice --> LogoutAll[Logout All Devices]
    
    SingleLogout --> LogoutRequest[POST /auth/logout]
    LogoutRequest --> BlacklistTokens[Blacklist Tokens]
    BlacklistTokens --> LogoutComplete[Clear Local Storage]
    
    LogoutAll --> LogoutAllRequest[POST /auth/logout-all]
    LogoutAllRequest --> RevokeAllTokens[Revoke All User Tokens]
    RevokeAllTokens --> LogoutComplete
    
    LogoutComplete --> LandingPage
    
    %% ================================
    %% ERROR HANDLING & EDGE CASES
    %% ================================
    
    Dashboard --> TokenRevoked{Token Blacklisted?}
    TokenRevoked -->|Yes| ForceLogout[Force Logout]
    ForceLogout --> ClearTokens
    
    %% Rate Limiting
    LoginForm --> RateLimit{Too Many Attempts?}
    RateLimit -->|Yes| AccountLock[Temporary Account Lock]
    AccountLock --> LockMessage[Show Lockout Message]
    LockMessage --> WaitPeriod[Wait for Unlock]
    WaitPeriod --> LoginForm
    
    %% Network Errors
    LoginSubmit --> NetworkError{Network Error?}
    NetworkError -->|Yes| RetryLogin[Show Retry Option]
    RetryLogin --> LoginForm
    
    %% ================================
    %% ADMIN FLOWS (Optional)
    %% ================================
    
    Dashboard --> AdminCheck{Is Admin?}
    AdminCheck -->|Yes| AdminPanel[Admin Panel]
    AdminPanel --> ManageVerifications[Manage Pending Verifications]
    AdminPanel --> ViewSecurityLogs[View Security Logs]
    AdminPanel --> ManageUsers[Manage User Accounts]
    AdminCheck -->|No| Dashboard
    
    %% ================================
    %% PASSWORD RESET FLOW (Future)
    %% ================================
    
    LoginForm --> ForgotPassword[Forgot Password Link]
    ForgotPassword --> ResetEmail[Enter Email for Reset]
    ResetEmail --> ResetRequest[POST /auth/password-reset/request]
    ResetRequest --> ResetEmailSent[Password Reset Email Sent]
    ResetEmailSent --> ResetLink[Click Reset Link in Email]
    ResetLink --> ResetForm[Enter New Password]
    ResetForm --> ResetSubmit[POST /auth/password-reset/confirm]
    ResetSubmit --> ResetSuccess[Password Reset Successfully]
    ResetSuccess --> LoginForm
    
    %% ================================
    %% DEVICE MANAGEMENT
    %% ================================
    
    Dashboard --> DeviceSettings[Device Settings]
    DeviceSettings --> ViewDevices[View Trusted Devices]
    ViewDevices --> RemoveDevice[Remove Trusted Device]
    RemoveDevice --> DeviceRemoved[Device Removed Successfully]
    DeviceRemoved --> ViewDevices
    
    %% ================================
    %% STYLING
    %% ================================
    
    classDef startEnd fill:#e1f5fe
    classDef process fill:#f3e5f5
    classDef decision fill:#fff3e0
    classDef error fill:#ffebee
    classDef success fill:#e8f5e8
    classDef security fill:#fce4ec
    
    class Start,LandingPage startEnd
    class LoginSuccess,VerifySuccess,MFASuccess,Dashboard success
    class LoginError,VerifyError,MFAError,AccountError error
    class DeviceCheck,TokenValid,CredentialsValid,MFAValid decision
    class GenerateMFA,SendMFAEmail,BlacklistTokens security
```