Electric — Proxy and Auth

import { ShapeStream } from '@electric-sql/client'

const stream = new ShapeStream({
  url: '/api/todos', // Points to your proxy, not Electric directly
})

Core Patterns

Tenant isolation with WHERE params

// In proxy route — inject user context server-side
const user = await getAuthUser(request)
originUrl.searchParams.set('table', 'todos')
originUrl.searchParams.set('where', 'org_id = $1')
originUrl.searchParams.set('params[1]', user.orgId)

Auth token refresh on 401

const stream = new ShapeStream({
  url: '/api/todos',
  headers: {
    Authorization: async () => `Bearer ${await getToken()}`,
  },
  onError: async (error) => {
    if (error instanceof FetchError && error.status === 401) {
      const newToken = await refreshToken()
      return { headers: { Authorization: `Bearer ${newToken}` } }
    }
    return {}
  },
})

CORS configuration for cross-origin proxies

// In proxy response headers
headers.set(
  'Access-Control-Expose-Headers',
  'electric-offset, electric-handle, electric-schema, electric-cursor'
)

Subset security (AND semantics)

Electric combines the main shape WHERE (set in proxy) with subset WHERE (from POST body) using AND. Subsets can only narrow results, never widen them:

-- Main shape: WHERE org_id = $1 (set by proxy)
-- Subset: WHERE status = 'active' (from client POST)
-- Effective: WHERE org_id = $1 AND status = 'active'

Even WHERE 1=1 in the subset cannot bypass the main shape's WHERE.

Common Mistakes

CRITICAL Forwarding all client params to Electric

Wrong:

url.searchParams.forEach((value, key) => {
  originUrl.searchParams.set(key, value)
})

Correct:

import { ELECTRIC_PROTOCOL_QUERY_PARAMS } from '@electric-sql/client'

url.searchParams.forEach((value, key) => {
  if (ELECTRIC_PROTOCOL_QUERY_PARAMS.includes(key)) {
    originUrl.searchParams.set(key, value)
  }
})
originUrl.searchParams.set('table', 'todos')

Forwarding all params lets the client control table, where, and columns, accessing any Postgres table. Only forward ELECTRIC_PROTOCOL_QUERY_PARAMS.

Source: examples/proxy-auth/app/shape-proxy/route.ts

CRITICAL Not deleting content-encoding and content-length headers

Wrong:

return new Response(response.body, {
  status: response.status,
  headers: response.headers,
})

Correct:

const headers = new Headers(response.headers)
headers.delete('content-encoding')
headers.delete('content-length')
return new Response(response.body, { status: response.status, headers })

fetch() decompresses the response body but keeps the original content-encoding and content-length headers, causing browser decoding failures.

Source: examples/proxy-auth/app/shape-proxy/route.ts:49-56

CRITICAL Exposing ELECTRIC_SECRET or SOURCE_SECRET to browser

Wrong:

// Client-side code
const url = `/v1/shape?table=todos&secret=${import.meta.env.VITE_ELECTRIC_SOURCE_SECRET}`

Correct:

// Server proxy only
originUrl.searchParams.set('secret', process.env.ELECTRIC_SOURCE_SECRET!)

Bundlers like Vite expose VITE_* env vars to client code. The secret must only be injected server-side in the proxy.

Source: AGENTS.md:17-20

CRITICAL SQL injection in WHERE clause via string interpolation

Wrong:

originUrl.searchParams.set('where', `org_id = '${user.orgId}'`)

Correct:

originUrl.searchParams.set('where', 'org_id = $1')
originUrl.searchParams.set('params[1]', user.orgId)

String interpolation in WHERE clauses enables SQL injection. Use positional params ($1, $2).

Source: website/docs/guides/auth.md

HIGH Not exposing Electric response headers via CORS

Wrong:

// No CORS header configuration — browser strips custom headers
return new Response(response.body, { headers })

Correct:

headers.set(
  'Access-Control-Expose-Headers',
  'electric-offset, electric-handle, electric-schema, electric-cursor'
)
return new Response(response.body, { headers })

The client throws MissingHeadersError if Electric response headers are stripped by CORS. Expose electric-offset, electric-handle, electric-schema, and electric-cursor.

Source: packages/typescript-client/src/error.ts:109-118

CRITICAL Calling Electric directly from production client

Wrong:

new ShapeStream({
  url: 'https://my-electric.example.com/v1/shape',
  params: { table: 'todos' },
})

Correct:

new ShapeStream({
  url: '/api/todos', // Your proxy route
})

Electric's HTTP API is public by default with no auth. Always proxy through your server so the server controls shape definitions and injects secrets.

Source: AGENTS.md:19-20

See also: electric-shapes/SKILL.md — Shape URLs must point to proxy routes, not directly to Electric. See also: electric-deployment/SKILL.md — Production requires ELECTRIC_SECRET and proxy; dev uses ELECTRIC_INSECURE=true. See also: electric-postgres-security/SKILL.md — Proxy injects secrets that Postgres security enforces.

Version

Targets @electric-sql/client v1.5.10.