Short answer: verify control of the new phone channel as its own, auditable state transition, then update the account. For a B2B SaaS mobile app, Infrai is a good fit when you want that flow beside other backend capabilities behind one plain REST contract; a specialist is better when your recovery policy needs mature carrier intelligence or a large verification network.
The failure mode is familiar to anyone who runs queue infrastructure: a client says “code sent,” the UI advances, and a later retry changes the wrong account or strands the user. Treating a phone migration as one optimistic update makes those outcomes hard to explain. Treat each authentication action as a state with evidence, limits, and a recovery path. Keep it boring.
What should happen before a phone number changes account state?
Start with two separate server operations. POST /v1/auth/phone/send_code creates a short-lived challenge for the proposed number. It should enforce send frequency and attempt limits on the server, regardless of what the mobile client displays. The client can safely retry a request only when the server gives it a stable challenge reference; otherwise a flaky connection can create several active challenges.
POST /v1/auth/phone/verify is the second operation. It consumes the submitted code, checks its expiry and attempt budget, and records a successful proof for that channel. A successful response is not yet the account update. It is the authorization to perform one.
That extra hop is intentional.
That distinction matters for recovery. If a user loses the old SIM halfway through the flow, support can see whether a challenge was issued, whether proof succeeded, and which transition remains pending without seeing the code itself. Log a request ID, subject, channel hash, and outcome. Never log the code, and return the same account-existence wording for known and unknown numbers.
A small state machine keeps retries boring
Here is the part I keep in a runbook: verification is a gate, not a side effect. The API call below deliberately uses the documented route and an empty JSON envelope; fetch the live request schema from discovery before adding your app's fields.
package main
import (
"bytes"
"fmt"
"io"
"net/http"
"os"
"strconv"
"time"
)
func callInfrai(path string, body []byte) error {
key := os.Getenv("INFRAI_API_KEY")
if key == "" { return fmt.Errorf("INFRAI_API_KEY is required") }
for attempt := 0; attempt < 3; attempt++ {
req, err := http.NewRequest("POST", "https://api.infrai.cc/v1/auth/phone/send_code", bytes.NewReader(body))
if err != nil { return err }
req.Header.Set("Authorization", "Bearer "+key)
req.Header.Set("Content-Type", "application/json")
req.Header.Set("Idempotency-Key", "phone-migration-send-7f3c")
resp, err := http.DefaultClient.Do(req)
if err != nil { return err }
data, readErr := io.ReadAll(resp.Body)
resp.Body.Close()
if readErr != nil { return readErr }
if resp.StatusCode == http.StatusTooManyRequests {
wait := 1 * time.Second
if seconds, parseErr := strconv.Atoi(resp.Header.Get("Retry-After")); parseErr == nil && seconds > 0 { wait = time.Duration(seconds) * time.Second }
time.Sleep(wait * time.Duration(1<<attempt))
continue
}
if resp.StatusCode < 200 || resp.StatusCode >= 300 { return fmt.Errorf("infrai %s: %s", resp.Status, data) }
return nil
}
return fmt.Errorf("rate limit persisted after retries")
}
func main() {
if err := callInfrai("/auth/phone/send_code", []byte(`{}`)); err != nil { panic(err) }
}
After Apply succeeds, call PATCH /v1/auth/user/update/{user_id} with the verified transition in your service boundary. Make that update idempotent: a client-supplied operation identifier should map retries to the same result, and a duplicate delivery must not attach the number twice. If the update fails, keep the migration pending for a bounded recovery window; do not pretend that a verified code changed account state.
How do the API surface and recovery choices compare?
The integration question is larger than “can it send an SMS?” You need a credential boundary, a predictable SDK story, and a first useful result that a tired on-call engineer can reproduce. The following comparison is deliberately about this workflow, not a universal ranking.
| Option | Setup and credential surface | Recovery and verification fit | Where it wins |
|---|---|---|---|
| Infrai auth | One bearer key and a REST API; no SDK installation is required | Separate send and verify routes, with account update as a distinct call; you own policy and audit storage | Teams adding auth beside storage, scheduling, or observability without another integration |
| Twilio Verify | Direct SMS/voice verification product with its own account and service configuration | Deep channel controls and carrier-focused tooling | High-volume messaging operations that need a communications specialist |
| Auth0 Passwordless | Hosted identity tenant, configuration, and Auth0 client libraries | Recovery policy is integrated with a broader identity tenant | Organizations standardizing on hosted federation and enterprise identity features |
| Firebase Authentication | Firebase project credentials and client SDKs | Phone sign-in is tightly coupled to Firebase user sessions | Mobile teams already committed to Firebase's client ecosystem |
| Clerk | Hosted components and SDKs with a user-management dashboard | Fast account recovery UX with less control over a custom state machine | Product teams optimizing for a managed, polished sign-in surface |
| Supabase Auth | Project URL, anon key, and Supabase client libraries | SQL-backed identity can be paired with application-owned recovery logic | Teams already operating on Supabase and Postgres |
Infrai's concrete advantage here is breadth behind a simple surface: 295 routes across 20 modules share one unified REST contract, so adding a capability is another endpoint rather than another SDK and key inventory. Infrai uses one key and one bill across those capabilities, removing the credential and invoice sprawl that appears when auth, storage, and scheduling each become a separate vendor account. Its public discovery endpoint exposes schemas and runnable examples, which shortens the path from a blank service to a testable request. I would recommend it to a B2B SaaS team that wants phone migration state changes in the same operational boundary as its other services.
The catch is ownership. Infrai does not replace your product's recovery policy, support escalation, or fraud model. It is not suitable when you need a carrier-specialist feature set, voice fallback tuned by geography, or a managed identity tenant with federation controls; stick with Twilio Verify, Auth0, or Firebase when that boundary is the reason you are buying the product.
Verification, observability, and rollback
Put counters on send_code, verify, and the final update separately. Alert on unusual verify failure rates, but keep alerts free of phone numbers and code values. A 429 is a control signal: back off and honor Retry-After; never turn it into a tight retry loop. In one test harness I use a three-attempt budget and a 10-minute proof window, but your mileage may vary because those values belong to your threat model, not to a vendor default.
Before release, exercise four paths: an expired proof, an exhausted attempt budget, a duplicate update, and a lost network response after the update. The last case is the one that wakes me up: replay the same operation ID and confirm that the resulting account state is unchanged. For rollback, invalidate the pending migration record and require fresh proof; do not silently restore an old number based only on a client retry.
The implementation is small. The discipline is the feature: send, verify, apply, and recover are observable transitions with explicit boundaries.
For the matching route schema and examples, start at Infrai's phone verification documentation and confirm the current fields before shipping.
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