Revamp auth module to support multiple providers linked to a single auth identity (#7521)

packages/modules/auth/integration-tests/__fixtures__/providers/default-provider.ts

@@ -23,10 +23,14 @@ export class AuthServiceFixtures extends AbstractAuthModuleProvider {
     try {
       authIdentity = await service.retrieve({
         entity_id: email,
-        provider: this.provider,
       })
 
-      if (authIdentity.provider_metadata?.password === password) {
+      // The provider has to be present, guaranteed by the retrieve filter above.
+      const providerIdentity = authIdentity.provider_identities?.find(
+        (pi) => pi.provider === this.provider
+      )!
+
+      if (providerIdentity.provider_metadata?.password === password) {
         return {
           success: true,
           authIdentity,
@@ -36,7 +40,6 @@ export class AuthServiceFixtures extends AbstractAuthModuleProvider {
       if (error.type === MedusaError.Types.NOT_FOUND) {
         const createdAuthIdentity = await service.create({
           entity_id: email,
-          provider: this.provider,
           provider_metadata: {
             password,
           },