7 replies

Session Management Type Inference

Hey everyone!

Need some help with Better Auth type inference for custom session data
I'm having an issue with TypeScript type inference when using customSession plugin with Better Auth. Here's my setup:

Client setup:

plugins: [customSessionClient<typeof auth>(), inferAdditionalFields<typeof auth>()]

plugins: [customSessionClient<typeof auth>(), inferAdditionalFields<typeof auth>()]

Server setup:

// Following the docs pattern with options passed to customSession
const options = { /* auth config */ } satisfies BetterAuthOptions;

export const auth = betterAuth({
  ...options,
  plugins: [
    customSession(async ({ user, session }) => {
      const userWithCompany = await prisma.user.findUnique({
        where: { id: Number(user.id) }, // Converting from old JWT auth which was setup to have the user.id as an INT, so I have the custom setting set for this to allow it
        include: { company: true },
      })
      return {
        user: { ...user, company: userWithCompany?.company || null },
        session,
      }
    }, options), // passing options as per docs
  ],
})

// Following the docs pattern with options passed to customSession
const options = { /* auth config */ } satisfies BetterAuthOptions;

export const auth = betterAuth({
  ...options,
  plugins: [
    customSession(async ({ user, session }) => {
      const userWithCompany = await prisma.user.findUnique({
        where: { id: Number(user.id) }, // Converting from old JWT auth which was setup to have the user.id as an INT, so I have the custom setting set for this to allow it
        include: { company: true },
      })
      return {
        user: { ...user, company: userWithCompany?.company || null },
        session,
      }
    }, options), // passing options as per docs
  ],
})

The Issue:

Works: When I call useSession() on the client, I get the full type with both:
Additional fields from user.additionalFields
Company data from my customSession

Doesn't work: Server-side type inference like:

export type User = typeof auth.$Infer.Session.user
// typeof auth.$Infer.Session.user.company doesn't exist here

export type User = typeof auth.$Infer.Session.user
// typeof auth.$Infer.Session.user.company doesn't exist here

The company property I'm adding in customSession isn't available in the inferred type on the server side (Which is where I want to define the type to use throughout the app), even though it works perfectly on the client after calling useSession().

Question: Is this expected behavior? Should custom session data only be available after calling useSession(), or am I missing something in my setup?

I'm following the docs here: https://www.better-auth.com/docs/concepts/session-management#customizing-session-response

Any insights would be super helpful!

Session Management Type Inference

Hey everyone!

plugins: [customSessionClient<typeof auth>(), inferAdditionalFields<typeof auth>()]

plugins: [customSessionClient<typeof auth>(), inferAdditionalFields<typeof auth>()]

Server setup:

// Following the docs pattern with options passed to customSession
const options = { /* auth config */ } satisfies BetterAuthOptions;

export const auth = betterAuth({
  ...options,
  plugins: [
    customSession(async ({ user, session }) => {
      const userWithCompany = await prisma.user.findUnique({
        where: { id: Number(user.id) }, // Converting from old JWT auth which was setup to have the user.id as an INT, so I have the custom setting set for this to allow it
        include: { company: true },
      })
      return {
        user: { ...user, company: userWithCompany?.company || null },
        session,
      }
    }, options), // passing options as per docs
  ],
})

// Following the docs pattern with options passed to customSession
const options = { /* auth config */ } satisfies BetterAuthOptions;

export const auth = betterAuth({
  ...options,
  plugins: [
    customSession(async ({ user, session }) => {
      const userWithCompany = await prisma.user.findUnique({
        where: { id: Number(user.id) }, // Converting from old JWT auth which was setup to have the user.id as an INT, so I have the custom setting set for this to allow it
        include: { company: true },
      })
      return {
        user: { ...user, company: userWithCompany?.company || null },
        session,
      }
    }, options), // passing options as per docs
  ],
})

export type User = typeof auth.$Infer.Session.user
// typeof auth.$Infer.Session.user.company doesn't exist here

export type User = typeof auth.$Infer.Session.user
// typeof auth.$Infer.Session.user.company doesn't exist here

Session Management Type Inference

Session Management Type Inference

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