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Flowglad ships with convenience adapters so you can construct the FlowgladServer with the authenticated customer from popular auth providers or from your own session logic. The examples below assume a Next.js project, but the same patterns apply anywhere you can create a FlowgladServer instance. Flowglad provides adapters for these auth providers:
  • Supabase Auth
  • Clerk
  • NextAuth
  • Better Auth

​
Supabase Auth

import { FlowgladServer } from '@flowglad/nextjs/server'
import { createClient } from '@/utils/supabase'

export const flowgladServer = new FlowgladServer({
  supabaseAuth: {
    // this must be the supabase server client
    client: createClient,
  },
})

​
Clerk

import { currentUser } from '@clerk/nextjs/server'
import { FlowgladServer } from '@flowglad/nextjs/server'

export const flowgladServer = new FlowgladServer({
  clerk: {
    currentUser,
  },
})

​
NextAuth

import { auth } from '@/auth' // your configured NextAuth client
import { FlowgladServer } from '@flowglad/nextjs/server'

export const flowgladServer = new FlowgladServer({
  nextAuth: {
    auth,
  },
})

​
Better Auth

import { auth } from '@/lib/auth'; // your Better Auth instance in auth.ts
import { headers } from 'next/headers';
import { FlowgladServer } from '@flowglad/nextjs/server';

export const flowgladServer = new FlowgladServer({
  betterAuth: {
    getSession: async () => auth.api.getSession({ headers: await headers() }),
  },
});

​
Custom session loaders

When you already have a helper that returns the signed-in user, pass it through getRequestingCustomer. 
import { FlowgladServer } from '@flowglad/nextjs/server'
import { getBespokeSession } from '@/utils/auth'

export const flowgladServer = new FlowgladServer({
  getRequestingCustomer: async () => {
    const session = await getBespokeSession()
    if (!session) return null

    return {
      externalId: session.id,
      name: session.name,
      email: session.email,
    }
  },
})
If you need to inspect the incoming request, derive the customer inside a factory that receives the request object. 
import { FlowgladServer } from '@flowglad/nextjs/server'
import { getBespokeSession } from '@/utils/auth'

export const createFlowgladServer = (request: Request) =>
  new FlowgladServer({
    getRequestingCustomer: async () => {
      const session = await getBespokeSession(request)
      if (!session) return null

      return {
        externalId: session.id,
        name: session.name,
        email: session.email,
      }
    },
  })

​
Custom auth example: Firebase

import { FlowgladServer } from '@flowglad/server'
import admin from 'firebase-admin'

admin.initializeApp()

export const flowgladServer = (request: Request) =>
  new FlowgladServer({
    getRequestingCustomer: async () => {
      const token = request.headers.get('authorization')?.replace('Bearer ', '')

      if (!token) return null

      try {
        const decodedToken = await admin.auth().verifyIdToken(token)

        return {
          externalId: decodedToken.uid,
          name: decodedToken.name || decodedToken.email!,
          email: decodedToken.email!,
        }
      } catch (error) {
        return null
      }
    }
  })

​
What happens at runtime?

Each adapter populates the customer payload that Flowglad needs to create purchases, subscriptions, and usage. Returning null simply means the request is unauthenticated. For edge or serverless environments, make sure the adapter you choose works with the runtime (e.g. Supabase Auth helpers are edge-ready).