Introduction

Managing multiple credentials across dozens of applications has become a security and usability nightmare for modern organizations. Single Sign-On (SSO) solves this by allowing users to access multiple applications with one set of credentials, while centralizing authentication for better security and user management.

Open source SSO providers have matured significantly, offering enterprise-grade features without vendor lock-in or hefty licensing costs. They provide the flexibility to customize authentication systems while maintaining robust security standards.

This guide explores top SSO providers some open source and others not so you gain a better view of the authentication landscape in 2025, helping you choose the right solution for your organization’s needs.

What is SSO?

Single Sign-On (SSO) is an authentication mechanism that allows users to access multiple applications and services using a single set of credentials. Instead of maintaining separate usernames and passwords for each application, users authenticate once and gain seamless access to all connected systems.

How SSO Works

The SSO process involves three key components:

Identity Provider (IdP): The central authentication service that verifies user credentials and issues authentication tokens. Examples include SuperTokens, Microsoft Entra ID, Auth0 Okta, and Keycloak.

Service Provider (SP): The application or service that users want to access. These rely on the IdP for user authentication rather than managing credentials directly.

Authentication Tokens: Secure digital certificates that prove a user’s identity. These tokens are passed between the IdP and SPs to grant access without re-entering credentials.

The SSO Authentication Flow

Step 1: First Login

User → Gmail → Identity Provider (login required)
User enters credentials → Token generated → Access granted

Step 2: Accessing Other Apps

User → Slack → Identity Provider (checks existing token)
Token valid → Instant access (no login needed)

Key Points:

• Login once at the Identity Provider
• Token shared across all connected applications
• No re-authentication needed for additional services

Benefits of Implementing SSO in Your Applications

Simplified User Experience

Password fatigue is real. Users often resort to weak, repeated credentials, changing as few characters as needed. SSO eliminates this burden by providing seamless access to all applications through a single authentication point.

Users can move fluidly between tools without interruption, this improved usability directly translates to higher productivity and user satisfaction.

Improved Security for End Users

SSO strengthens security by addressing the weakest link in most systems: password management. When users only need to remember one strong password, they’re more likely to create and maintain secure credentials.

SSO enables organizations to enforce consistent security policies across all applications, including multi-factor authentication (MFA), password complexity requirements, and session management. Centralized authentication also provides better audit trails and makes it easier to detect suspicious login patterns or unauthorized access attempts.

For compliance-heavy industries like healthcare or finance, SSO supports regulatory requirements by providing detailed access logs and ensuring consistent security controls across all systems.

Operational Efficiency

IT teams spend countless hours on password related issues, account lockouts, and access problems that consume significant resources. SSO dramatically reduces these support tickets by eliminating most password management issues.

When employees leave or change roles, administrators can instantly revoke or modify access across all connected applications from a single point, rather than manually updating dozens of individual systems. This centralized user management reduces security risks and administrative overhead.

The time savings extend beyond IT support. Employees spend less time on authentication related tasks, and onboarding new users becomes streamlined when they gain immediate access to all necessary tools through one account setup.

Common SSO Protocols

SSO implementations rely on standardized protocols to securely exchange authentication data between identity providers and applications.

SAML (Security Assertion Markup Language)

SAML is an XML-based protocol that exchanges authentication data via assertions-structured XML documents containing user identity information. When a user logs in, the identity provider creates a SAML assertion and sends it to the service provider for access.

Best for enterprise applications and legacy systems requiring detailed user attributes.

OAuth 2.0

OAuth is an authorization framework that uses access tokens to grant limited access to user resources without exposing passwords. Applications receive tokens from the authorization server to access protected resources.

Ideal for modern web and mobile applications, API integrations, and granular access control.

OpenID Connect

OpenID Connect builds on OAuth 2.0 to add an authentication layer by providing ID tokens that contain user identity information alongside OAuth’s access tokens.

Perfect for applications needing both user authentication and API access.

Key Features to Look for in an SSO Provider

Integration Capabilities

Your SSO provider must connect seamlessly with existing systems and third-party applications. Look for solutions that support multiple protocols (SAML, OAuth, OpenID Connect) and offer pre-built connectors for popular apps.

API availability is crucial for custom integrations and automation. The provider should offer comprehensive documentation and SDKs for different programming languages.

Scalability

The SSO solution should handle growth in users and applications without performance degradation. Consider providers that offer horizontal scaling capabilities and can support your organization’s projected growth over the next few years.

Performance metrics like response times and uptime guarantees indicate how well the system will handle increased load during peak usage periods.

User Experience Customization

The ability to customize login interfaces to match your branding creates a cohesive user experience. Look for providers that allow custom logos, colors, and domain names to maintain brand consistency.

Advanced customization options include custom authentication flows, conditional access policies, and personalized user dashboards that align with your organization’s workflow.

Analytics and Reporting

Monitoring user access patterns helps detect anomalies and security threats while providing insights into application usage. Essential reporting features include login frequency, failed authentication attempts, and access patterns across different applications.

Real-time alerts for suspicious activities and comprehensive audit logs support both security monitoring and compliance requirements.

This process uses standard protocols like SAML, OAuth 2.0, or OpenID Connect to ensure secure communication between all components.

Comparing SSO Providers

Each provider addresses different organizational needs. Consider your technical requirements, budget constraints, existing infrastructure, and team expertise when making your selection.

Here’s a table comparing ideal use cases:

Implementing SSO with SuperTokens

SuperTokens takes a developer first approach to SSO implementation, turning what’s traditionally a complex integration into a straightforward process. Unlike heavyweight enterprise solutions, SuperTokens provides flexible, open-source authentication that scales from startup MVPs to enterprise deployments.

SuperTokens Core serves as the main authentication service handling all the auth logic. It can be self-hosted or use SuperTokens service. The backend sdk integrates with your APIs exposing the auth endpoints, and the frontend sdk manages the auth UI and session handling on the client side.

Backend Details

The connection_uri is the link between your backend and the SuperTokens Core service. For dev environments you can make use of the demo instance:

connection_uri="https://try.supertokens.com"

In production, this should be your self-hosted instance or the managed service endpoint.

For a Python/FastAPI implementation, the complete configuration structure requires both connection details and app information:

# config.py
supertokens_config = SupertokensConfig(
    connection_uri="https://try.supertokens.com"
)

app_info = InputAppInfo(
    app_name="SuperTokens Proof of Concept",
    api_domain=get_api_domain(),
    website_domain=get_website_domain(),
    api_base_path="/auth",
    website_base_path="/auth"
)

In the same file you can add SuperTokens recipes, these recipes provide expanded pre-built auth features. Let’s use the Social Login Recipe to add Github SSO as a login method.

# config.py
from supertokens_python import InputAppInfo, SupertokensConfig, init
from supertokens_python.recipe import dashboard, session, thirdparty, userroles
from supertokens_python.recipe.thirdparty.provider import (
    ProviderClientConfig,
    ProviderConfig,
    ProviderInput,
)


def get_api_domain() -> str:
    api_port = str(3001)
    api_url = f"http://localhost:{api_port}"
    return api_url

def get_website_domain() -> str:
    website_port = str(3000)
    website_url = f"http://localhost:{website_port}"
    return website_url

supertokens_config = SupertokensConfig(
    connection_uri="https://try.supertokens.com"
)

app_info = InputAppInfo(
    app_name="SuperTokens Proof of Concept",
    api_domain=get_api_domain(),
    website_domain=get_website_domain(),
    api_base_path="/auth",
    website_base_path="/auth"
)

recipe_list = [
    session.init(),
    dashboard.init(),
    userroles.init(),
    thirdparty.init(
        sign_in_and_up_feature=thirdparty.SignInAndUpFeature(
            providers=[
                ProviderInput(
                    config=ProviderConfig(
                        third_party_id="github",
                        clients=[
                            ProviderClientConfig(
                                client_id="YOUR_CLIENT_ID_FROM_GITHUB",
                                client_secret="YOUR_CLIENT_SECRET_FROM_GITHUB"
                            )
                        ]
                    )
                ),
                ]
        )
    )
]

init(
    supertokens_config=supertokens_config,
    app_info=app_info,
    framework="fastapi",
    recipe_list=recipe_list,
    mode="asgi",
    telemetry=False
)

The get_api_domain(), and get_website_domain() must match your deployment urls to prevent cors issues, while the base paths define where SuperTokens routes are mounted.

Frontend Details

SuperTokens provides pre-built UI components and an interface for custom UIs, more information can be found in the docs.

Using the supertokens-web-js sdk we’ll add auth functionality to our angular frontend.

Note the providers, we currently only specify github but SuperTokens has support for several others e.g Apple, Google, Discord. Check docs for a complete list of growing providers.

// config.ts
import SuperTokens from "supertokens-web-js";
import Session from "supertokens-web-js/recipe/session";

const isMultitenancy = false;

export function getApiDomain() {
    const apiPort = 3001;
    const apiUrl = `http://localhost:${apiPort}`;
    return apiUrl;
}

export function getWebsiteDomain() {
    const websitePort = 3000;
    const websiteUrl = `http://localhost:${websitePort}`;
    return websiteUrl;
}

export function initSuperTokensUI() {
    (window as any).supertokensUIInit("supertokensui", {
        appInfo: {
            websiteDomain: getWebsiteDomain(),
            apiDomain: getApiDomain(),
            appName: "SuperTokens Proof of Concept",
            websiteBasePath: "/auth",
            apiBasePath: "/auth",
        },
        
        recipeList: [
            (window as any).supertokensUISession.init(),
            (window as any).supertokensUIThirdParty.init({
                signInAndUpFeature: {
                    providers: [
                        (window as any).supertokensUIThirdParty.Github.init(),
                    ],
                },
            })
        ],
        getRedirectionURL: async (context: any) => {
            if (context.action === "SUCCESS") {
                return "/dashboard";
            }
            return undefined;
        },
    });
}

export function initSuperTokensWebJS() {
    SuperTokens.init({
        appInfo: {
            appName: "SuperTokens Proof of Concept",
            apiDomain: getApiDomain(),
            apiBasePath: "/auth",
        },
        recipeList: [
            Session.init()
        ]
    });

    if (isMultitenancy) {
        initTenantSelectorInterface();
    }
}

export async function initTenantSelectorInterface() { };;

Lastly we need to update the FastAPI middleware file app.py to ensure proper request interception.

# app.py
import uvicorn

from fastapi import FastAPI, Depends
from starlette.middleware.cors import CORSMiddleware

from supertokens_python import init, get_all_cors_headers
from supertokens_python.framework.fastapi import get_middleware
from supertokens_python.recipe.session import SessionContainer
from supertokens_python.recipe.session.framework.fastapi import verify_session
from supertokens_python.recipe.multitenancy.asyncio import list_all_tenants

import config

# SuperTokens init should happen in config.py
app = FastAPI(
    title="SuperTokens Proof of Concept",
    # Disable automatic trailing slash redirection
    redirect_slashes=False
)
app.add_middleware(get_middleware())

async def get_session_info(s: SessionContainer = Depends(verify_session())):
    return {
        "sessionHandle": s.get_handle(),
        "userId": s.get_user_id(),
        "accessTokenPayload": s.get_access_token_payload(),
    }

# Add routes for both with and without trailing slash
app.get("/sessioninfo")(get_session_info)
app.get("/sessioninfo/")(get_session_info)

The verify_session() dependency automatically validates sessions and refreshes tokens when needed. For custom session validation logic, you can access the SessionContainer object which provides methods to read and modify session data.

If you would like to see a full end-to-end solution you can run the following cmd to generate an example app

npx create-supertokens-app --appname=sso-with-supertokens --recipe=thirdparty --frontend=angular --backend=python

Why SuperTokens for SSO?

Open Source Flexibility: Self-host for free with complete control over your authentication infrastructure, or use their managed service for hassle-free maintenance. No vendor lock-in means you own your user data and can customize every aspect of the authentication flow. Unlike Auth0 or Okta where you’re at the mercy of their feature roadmap, with SuperTokens you can fork the core and add that weird edge case your enterprise client demands.

Modern Protocol Support: SuperTokens handles OAuth 2.0, OpenID Connect, and even SAML through clever integrations. The framework abstracts away protocol complexity while maintaining compliance with industry standards. Need to support that ancient LDAP system? You can build a custom provider on top of SuperTokens’ extensible architecture. The recipe system means you’re not dragging along authentication methods you’ll never use, just include what you need.

Developer Experience: Pre-built UI components get you running in minutes, while comprehensive SDKs for Node.js, Python, and Go provide the flexibility to build custom flows. Clean easy to understand docss with plenty of examples. Error messages tell you what went wrong AND how to fix it. The three-tier architecture means your debugging stays in familiar territory: your own backend logs, not some opaque third-party service.

Session Management That Just Works: Automatic token refresh, CSRF protection, and secure cookie handling come built-in, you don’t need a PhD in web security to implement auth correctly. The SDK handles the gnarly bits like token rotation and concurrent request handling that typically cause race conditions in homegrown solutions.

Cost-Effective Scaling: The self-hosted option remains free regardless of user count. Even the managed service pricing stays reasonable as you grow, avoiding the painful pricing tiers of traditional auth providers. That surprise bill when you hit 10,001 monthly active users? Not happening here. Your auth costs become predictable infrastructure costs, not per-user taxes.

True Framework Agnostic: While our examples use Angular and Python, SuperTokens genuinely works with any stack. React, Vue, Svelte on the frontend? Covered. Express, FastAPI, Rails, Laravel on the backend? All supported. The standardized API means switching frameworks doesn’t mean rewriting your entire auth layer.

Best Practices for SSO Implementation

User Education

Rolling out SSO without user communication is like deploying without release notes: technically it works, but everyone’s confused.

Before launch: Send a simple email explaining the benefits: one password, faster access, better security. Skip the 20-page policy document.

During rollout: Provide visual guides showing the new login flow. Include screenshots of what users will actually see. Cover common scenarios like mobile access and timeout behavior.

After launch: Expect support tickets in the first 48 hours. Most issues? Users trying old passwords or not understanding redirects. A good FAQ cuts tickets by 80%.

Security Considerations

SSO concentrates risk: one compromised account means total access. MFA isn’t optional.

MFA Strategy: Implement at the SSO level, not per-app. Skip SMS (vulnerable to SIM swapping) in favor of push notifications, hardware tokens, or biometrics.

Monitor Everything:

• Flag unusual login patterns (Bob logging in from three continents in an hour)
• Revoke access immediately when employees leave
• Set 8-hour session timeouts with sliding extensions
• Alert on failed login spikes (3 failures = forgotten password, 300 = attack)

Compliance and Governance

Centralized auth means centralized audit logs. When auditors arrive, you pull one report instead of diving through dozens of application logs.

Industry Requirements:

• HIPAA: Auto-logoff and encryption
• SOC 2: Access controls and monitoring
• GDPR: Data minimization in user attributes

Governance Basics:

• Define who approves new SSO integrations
• Schedule quarterly access reviews
• Document which attributes each app receives
• Create break-glass procedures for SSO outages

Document your architecture with the why, not just the what: “We chose SAML for legacy app X because their OAuth implementation was held together with duct tape.”

Conclusion

Open source SSO has matured beyond “good enough” to genuinely excellent. Whether you need Keycloak’s enterprise features or SuperTokens’ developer experience, there’s a solution that fits.

Choose based on your actual needs: technical expertise, integrations, scale, and compliance. Start small with a pilot, gather feedback, iterate. Perfect authentication on day one isn’t the goal, building a sustainable system is.

Your users get fewer passwords. Security gets centralized monitoring. Developers skip building another login system. Everyone wins.

Ready to simplify authentication? Pick a provider, build a proof of concept, and watch your password reset tickets disappear. The future of auth is open, flexible, and refreshingly straightforward.