Composio vs Arcade vs Nango: AI Agent Authentication in 2026

Last week I spent two days untangling an authentication problem that nearly shipped to production on ServiceBot AI Helpdesk, one of the AI products we run at Warung Digital Teknologi (wardigi.com). The agent could read a customer's Gmail thread, draft a reply, and push a refund through Stripe — all in one tool-calling loop. The problem? Every one of those calls used a single shared service-account token. One support rep's agent could, in theory, act on another rep's connected mailbox. That is the exact failure mode the new generation of AI agent authentication platforms exists to kill.

If you are building agents that touch real user data through Gmail, Slack, Notion, Stripe, or GitHub, you have hit this wall or you are about to. The question is no longer "how do I call the OpenAI function-calling API" — it is "whose credentials does this tool call run under, and can I prove it later in an audit." This comparison breaks down the three platforms I evaluated for our own stack — Composio, Arcade, and Nango — plus where WorkOS and Merge fit, and which one I would actually pick for each scenario.

Why agent authentication became its own category in 2026

Through 2024 and most of 2025, "tool use" meant you hardcoded an API key in an environment variable and the agent called the API. That works for a single-user script. It collapses the moment you have multiple humans behind the same agent, because you need three things a static key cannot give you:

• Per-user identity — the agent must act as this user, with this user's permissions, not a god-mode service account.
• Token lifecycle — OAuth access tokens expire in an hour. Refresh, rotation, and secure storage have to happen without dumping a refresh token into your agent's prompt context (where the LLM could leak it).
• Auditability — when a regulator or a customer asks "who deleted that record," you need an immutable log tying the action to a real person, not "the bot did it."

The accelerant was Anthropic's Model Context Protocol (MCP). MCP standardized how agents discover and call tools, and the 2026 revision of the spec settled on OAuth 2.1 as its authorization primitive. That single decision turned auth from a per-integration afterthought into a composable layer — and created a market for platforms that handle it properly. MarkTechPost ran a dedicated roundup of these platforms on May 25, 2026, which is a decent signal that this is now a recognized buying category, not a niche concern.

The three architectures, side by side

The confusing part when you first research this space is that Composio, Arcade, and Nango all say "we do auth for AI agents," yet they solve genuinely different problems. Here is the distinction that took me a full evaluation cycle to internalize.

Composio — when you want connectors yesterday

Composio is a hosted catalog of roughly 1,000 pre-built tools. The pitch is time-to-production: instead of writing and maintaining a Gmail tool, a Slack tool, and a Jira tool — each with its own auth dance, schema, retry logic, and rate-limit handling — you import them. Managed OAuth is bundled in, but it is not the headline; the connectors are.

In my experience, this is the right call when the bottleneck is breadth. When we prototyped BizChat Revenue Assistant — an agent that reads a sales rep's CRM, calendar, and email to surface next-best-actions — the value was in covering eight SaaS tools fast, not in customizing the auth flow. Composio got a working multi-tool agent running in an afternoon. The tradeoff I have seen in production: you are buying into a hosted catalog, the enterprise pricing is not published (you talk to sales), and you have less control over the exact auth semantics than a code-first tool gives you. If your differentiator is "we integrate with everything," Composio earns its keep. If your differentiator is "we are SOC 2 / HIPAA airtight on identity," it is not the sharpest tool for that specific job.

Arcade — when every tool call must be identity-aware

Arcade approaches the problem from the opposite end. It bills itself as the first MCP runtime purpose-built for agent authorization, and the entire design centers on the fact that a tool call should execute with the credentials and permissions of the human who requested it — never a shared account.

Concretely, Arcade handles per-user OAuth, just-in-time consent (the user gets prompted to authorize a scope the moment the agent needs it, via URL elicitation), token vaulting so credentials never enter the LLM's context, policy intersection, and an immutable audit trail — all as native runtime capabilities rather than bolt-ons. It runs as a managed cloud service or self-hosted inside your own VPC, with on-prem MCP server support for reaching private resources.

This is the architecture that maps to the ServiceBot problem I opened with. The reason our shared-token design was dangerous is precisely what Arcade eliminates: per-user credential isolation means each support rep's agent operates with that rep's own tokens, so user attribution survives all the way into the audit log. If you are in a regulated industry — finance, healthcare, accounting — where "the bot did it" is not an acceptable answer to a compliance question, this is the one I would shortlist first. The cost model is execution/usage-based rather than per-seat, which is fairer for spiky agent workloads but means you should estimate call volume before committing.

Nango — when you want code-first control and an exit hatch

Nango sits at the infrastructure layer. It handles OAuth token storage, refresh cycles, and authenticated proxying across 800+ APIs, then deliberately gets out of your way. Unlike Composio, it does not hand you pre-built agent tool schemas or agent-aware error handling — you build the tool layer yourself. The trade is explicit: more wiring in exchange for more control.

The thing that makes Nango interesting for a small shop like ours is that it is open source under the Elastic License and the self-hosted version is free, covering managed OAuth for 700+ APIs plus an authenticated proxy and a Connect UI for end-user authorization. You spin it up with Docker Compose and you own the deployment. The catch — and this matters for budgeting — is that the production-grade features (durable data syncs, actions, full observability) live in the Enterprise self-hosted plan, which is an annual license plus usage fees. So "free" gets you auth and proxying; the sync engine is the paid part.

From 11+ years building integrations, my read is that Nango is the pick when you have engineers who want to own the tool layer and you care about avoiding vendor lock-in. It is the most "infrastructure" of the three, in the good sense.

The OAuth 2.1 shift, and why it matters for your code

It is worth slowing down on the OAuth 2.1 point because it changes how you should think about lock-in. When MCP settled on OAuth 2.1 as its authorization primitive, it made the auth layer composable rather than monolithic. In practice that means you can mix an authorization server from one vendor, a gateway from another, and an integration catalog from a third, instead of swallowing one company's full stack. That is a meaningful difference from the 2024 world, where choosing an integration platform usually meant adopting its proprietary auth model end to end.

The concrete upgrades OAuth 2.1 brought over 2.0 are the ones that matter for agents: PKCE is now mandatory for all clients (it closes the authorization-code interception hole that bit a lot of early SDK integrations), implicit flow is dead, and refresh-token rotation is the expected default. When I audited our own integrations against this, the single most common gap was long-lived non-rotating refresh tokens sitting in a database — exactly the thing 2.1 pushes you away from. If you take one operational habit from this article, make it this: rotate refresh tokens, and store them somewhere the model can never read.

The other thing the spec settled is delegated access via OIDC — the agent does not impersonate the user with the user's raw password-equivalent, it acts on a scoped, consented grant. That is the technical foundation under every "per-user identity" claim in this article. Without it, "the agent acts as the user" is just a shared token with extra steps.

Build vs. buy: should you even use a platform?

A fair question before spending money: can you just build this yourself? You can. OAuth is a documented protocol and storing tokens in Postgres is not exotic. I have built exactly that for single-integration, single-user tools and it was the right call — adding a platform there would have been over-engineering.

The math flips at scale, and it flips along a curve that is easy to underestimate. The cost of DIY auth is not the first integration; it is the tenth, multiplied by every edge case each API throws. Google's OAuth consent screen verification, Slack's rotating tokens, Salesforce's per-org instance URLs, Stripe Connect's account-scoping — each is a small project, and each breaks differently when a token expires. Across the integrations we have shipped, the maintenance tax of homegrown auth was consistently the thing nobody budgeted for and everybody paid. The platforms are essentially selling you out of that maintenance curve. My rule of thumb: under three integrations and one user class, build it; past that, buy the auth layer and spend your engineering time on the agent logic that is actually your product.

Security failure modes these platforms prevent

It helps to name the specific bad outcomes, because "more secure" is too vague to act on. Four failure modes show up repeatedly in agent systems, and each platform addresses them differently:

• Confused-deputy — the agent uses its own elevated privileges to do something the requesting user should not be allowed to do. Per-user OAuth (Arcade's core stance) kills this because the call literally runs with the user's scopes, not the agent's.
• Token leakage into context — a credential ends up in the prompt or the model's output, where it can be logged, cached, or exfiltrated. Token vaulting (all three platforms) keeps secrets out of the LLM entirely.
• Over-broad scopes — the agent requests full_access when it needed read:messages. Just-in-time consent narrows the grant to what the current action needs, when it needs it.
• Audit gaps — an action happened but you cannot tie it to a person. Immutable, identity-attributed logs (native in Arcade, Enterprise-tier in Nango) close this.

When I map our ServiceBot near-miss onto this list, it was a confused-deputy problem dressed up as a convenience feature. The shared service account was the elevated privilege, and the agent was the confused deputy wielding it. No amount of prompt engineering fixes that — it is an identity architecture issue, full stop.

Where WorkOS and Merge fit

Two more names show up constantly in this research, so it is worth placing them. WorkOS comes at agent auth from the enterprise SSO/directory direction — if you already use it for human SSO, SCIM, and audit logs, its agent-authentication features extend that same identity backbone to bots. Merge is a unified-API play: one integration gives you a category of tools (all HR systems, all CRMs) behind a normalized schema, with OAuth handled. Merge optimizes for "I never want to touch a vendor-specific API again," which is a different goal than fine-grained per-call agent authorization.

A decision matrix you can actually use

What I would do today, concretely

If I were rebuilding ServiceBot's auth from scratch this month, here is the actual plan. I would put Arcade's runtime in front of the high-sensitivity tools — anything that moves money or touches PII (Stripe, the mailbox, the CRM write path) — because per-user OAuth and immutable audit are non-negotiable there. For the low-risk read-only enrichment tools (looking up a public package version, fetching weather, hitting an internal docs search), the overhead of a full authorization runtime is not worth it, and a simpler Composio-style managed connector or even a direct call is fine. Mixing layers by risk tier, rather than forcing one platform to do everything, is the pattern I keep landing on across our seven aggregator sites and client builds.

Two practical warnings from doing this in production. First: do not let any refresh token reach the LLM's context window. It feels convenient to pass credentials inline; it is a leak waiting to happen, and all three platforms exist partly to prevent it — use the vault. Second: test the token-refresh path explicitly. The bug that bites you is not day one; it is hour two, when the first access token expires mid-conversation and a half-built integration silently drops the call. Write a test that fast-forwards past expiry before you ship.

FAQ

Is MCP required to use any of these?

No. Arcade is built around MCP and benefits most from it, but Composio and Nango work with or without MCP — they predate the spec's auth convergence and support direct SDK use. MCP is becoming the common transport, not a hard dependency.

Can I just use OAuth myself and skip the platform?

You can, and for a single integration with one user it is reasonable. The platforms earn their cost at multi-user, multi-tool scale, where token storage, refresh, rotation, per-user isolation, and audit become a real engineering project rather than a weekend script.

Which is cheapest to start?

Nango's free self-hosted tier, which covers OAuth for 700+ APIs. The caveat is that durable syncs, actions, and full observability are gated behind its Enterprise plan, so "free" means auth and proxying, not the whole platform.

Does per-user auth slow down the agent?

The just-in-time consent flow adds a one-time prompt the first time a user authorizes a scope. After that, cached vaulted tokens make subsequent calls effectively as fast as a static key, with refresh handled transparently in the background.

Bottom line

These three are not really competitors so much as three answers to three different questions. Composio answers "how do I integrate with everything fast." Arcade answers "how do I make every tool call identity-aware and auditable." Nango answers "how do I own my auth infrastructure without lock-in." Pick the question that is actually blocking you. For us, the lesson from the ServiceBot near-miss was that the moment more than one human stands behind an agent, identity stops being a feature and becomes the architecture — and 2026's tooling finally treats it that way.