Let’s start with the plainest possible definition before adding any complexity.

A login flow in Keycloak is an ordered sequence of individual authentication steps that a user must go through to prove their identity. Instead of authentication being one single, fixed action — “type a password” — Keycloak treats it as a small, configurable pipeline made of separate, swappable pieces, each one checking something specific: a password, a one-time code, a trusted device, or even a decision based on conditions like the user’s role or location.

Login flows are one of Keycloak’s most powerful and most distinctive features. Where many simpler systems hard-code “username and password, that’s it,” Keycloak lets administrators visually design exactly what a user must do to sign in — and different flows can be applied to different situations, like a stricter flow for administrators than for regular customers.

Before flows existed as a concept, authentication logic was usually rigid and hard to change.

In many older or simpler systems, “how login works” is baked directly into the application’s code. If a company later decides it wants to add multi-factor authentication, or skip the password step for trusted devices, or require an extra check only for admin accounts, a developer has to go dig into the code and rewrite the login logic by hand — risky, slow, and error-prone for something as sensitive as authentication.

Keycloak’s login flow system solves this by turning authentication into configuration instead of code. Administrators can rearrange, add, remove, or make steps conditional entirely through the admin console, without touching a single line of application code. This is what makes login flows so valuable in real-world identity management — they let security requirements evolve quickly as an organization’s needs change.

Just like the recipe-card analogy, let’s meet the actual pieces that make up a flow.

Flow

A flow is the top-level container — a named sequence like “Browser,” “Direct Grant,” or a custom flow an administrator built, such as “High-Security Admin Login.”

Sub-Flow

A flow can contain a nested mini-flow inside it, grouping a few related executions together — for example, a “Multi-Factor” sub-flow containing both “OTP Form” and “WebAuthn” as alternative options within it.

Execution

Each individual line inside a flow is an execution — a single, specific checkpoint, like “Username Password Form” or “OTP Form.”

Authenticator

Behind every execution sits an authenticator — the actual logic that performs the check. Keycloak ships with many built-in authenticators, and custom ones can be added by developers.

Zooming out to see how login flows connect to the rest of a realm’s configuration.

Now let’s trace exactly what happens internally when a real user tries to log in.

When someone attempts to log in, Keycloak’s authentication engine loads the relevant flow and walks through its executions from top to bottom, evaluating each one’s requirement level as it goes.

sequenceDiagram
    participant U as User
    participant App as Application
    participant KC as Keycloak Engine
    U->>App: Attempt to access app
    App->>KC: Redirect to login
    KC->>U: Show Step 1 (Username/Password)
    U->>KC: Submit credentials
    KC->>KC: Evaluate requirement + condition
    KC->>U: Show Step 2 (OTP, if required)
    U->>KC: Submit OTP code
    KC->>KC: All required steps passed
    KC-->>App: Issue tokens, redirect back
    App-->>U: Access granted
        

A broader view of how a login flow fits inside the entire authentication lifecycle.

flowchart TD
    A[Login Flow Defined in Admin Console] --> B[Flow Assigned to Realm or Client]
    B --> C[User Initiates Login]
    C --> D[Engine Executes Flow Step by Step]
    D --> E{All Required Steps Passed?}
    E -->|Yes| F[Session Created and Tokens Issued]
    E -->|No| G[Login Denied, Attempt Logged]
        

Notice that the flow itself is designed once, ahead of time, by an administrator — but it’s executed fresh, from the beginning, for every single login attempt. This separation between “designing the process” and “running the process” is exactly what makes login flows reusable and easy to reason about.

Keycloak comes with several ready-made flows out of the box, each serving a different purpose.

This single setting is what gives login flows their real power and flexibility.

Every execution inside a flow has a requirement level, and understanding these four options is the key to designing a flow correctly.

Flexibility is powerful, but it comes with real design responsibility.

Since a login flow is literally the front door, small design mistakes here have outsized consequences.

Avoid Weak Alternative Paths

If “password” and “email magic link” are both Alternative options, and the email account is compromised, the attacker can simply bypass the password entirely. Every Alternative branch should be roughly as strong as the others.

Use Conditional Steps for Risk-Based Authentication

A well-designed flow can require extra verification only in higher-risk situations — an unfamiliar device, an admin role, or a login from an unusual location — rather than annoying every single user with the strictest possible checks all the time.

Protect the Recovery Flow as Strongly as the Login Flow

The “Reset Credentials” flow is often overlooked, yet it’s frequently the easiest path for an attacker — if resetting a password is weaker than logging in directly, attackers will target the reset flow instead.

A flow’s design only matters if you can also see how it behaves in the real world.

Some flow designs age gracefully. Others quietly become maintenance nightmares.

A practical checklist for anyone designing or reviewing a login flow.

Seeing login flows applied to concrete situations makes the concept click.

Across all of these, the underlying mechanism never changes — only the executions chosen, their order, and their requirement levels. This is precisely why login flows are considered one of the most reusable and powerful design tools inside Keycloak.

Yes. A specific flow can be bound to an individual client application, so one app can require stricter authentication than another, even though both belong to the same realm.

The entire login attempt fails immediately. Required steps must all succeed — there’s no way to proceed past a failed Required execution.

It’s generally safer to duplicate it first and edit the copy. This keeps a known-working fallback available in case the customization introduces an unexpected issue.

An Alternative step is one of several options a user can freely choose among to satisfy that part of the flow. A Conditional step isn’t a user choice at all — it’s automatically included or skipped based on a rule, such as the user’s role.

Yes. Keycloak supports custom authenticators, which developers can build and register, allowing entirely new verification methods to be plugged into any flow alongside the built-in ones.

Yes, the engine evaluates executions strictly in the order they’re arranged. This is why, for example, a password check is typically placed before an OTP check — the user’s basic identity should be confirmed before asking for a second factor.

A login flow in Keycloak turns authentication from a single, rigid step into a configurable, ordered sequence of individual checks — each one an execution backed by an authenticator, each one marked as Required, Alternative, Conditional, or Disabled. This design lets administrators reshape how users prove their identity entirely through configuration, applying different strictness levels to different applications, adding new authentication methods without writing code, and building proportional, risk-based rules that only demand extra verification when it’s actually warranted. Like any powerful tool, flows require careful design — a poorly placed Alternative branch or an untested Conditional path can quietly weaken security instead of strengthening it. Understood well, though, login flows are one of the clearest examples of how Keycloak turns something as sensitive as authentication into something transparent, flexible, and genuinely manageable.