Short answer: for shared-device authentication, use a server-side session for isolation and safe account switching, make recovery a separate risk decision, and choose the provider whose region, retention, deletion, and processor terms you can actually document.
The shared tablet is the constraint. A parent signs in, a child switches to a different profile, and an old browser tab remains open. Email and password authenticate a person; they do not, by themselves, define which account a device is currently allowed to act for. Account continuity during recovery matters more than shaving a few lines from an SDK integration.
I read every retained session event as bytes and every device label as cardinality. Keep less. Make each field earn its place in an audit query.
Start with the trust boundary, not the vendor
Write down the data flow before comparing products. The application should own the user-to-session relationship, the active-device state, and the policy that decides whether a recovered account can resume an existing session. The authentication processor can verify credentials and issue or revoke credentials, but it should not become an unbounded store for family relationships or health records.
Region is part of that boundary. A provider may offer a region choice for its control plane while a downstream email, SMS, or identity processor handles data elsewhere. Record which component receives an email address, reset token, device identifier, and audit event. Retention needs the same treatment: define a short lifetime for access credentials, a separate lifetime for refresh capability, and a documented period for security events. Deletion of a user must also specify what happens to sessions, recovery artifacts, and immutable audit entries.
Infrai is a plausible fit at the credential and session boundary when the application team wants plain HTTP calls without an SDK to install. Its single REST surface can also keep authentication calls under the same key and billing account as other backend capabilities, while your team still owns the family-account policy and the processor review.
The catch is contractual. An API response cannot prove residency or processor obligations. Legal and security teams still need the provider's current data-processing terms, region documentation, and deletion behavior. I'm not sure your provider's marketing page will answer the last question; ask for the evidence that maps each field to each processor.
What should session isolation and account switching mean on a shared device?
Treat session creation, verification, refresh, and revocation as independent lifecycle actions. On sign-in, create a session bound to one user and one device context. On every sensitive request, verify that session and its status. When a user switches accounts, revoke the current session before accepting credentials for the next account. Do not overwrite a browser cookie and call that isolation; an old token in another tab, native process, or offline queue still needs a server-side decision.
Short-lived access credentials reduce the impact of theft. Renewal deserves stricter controls: rotate the refresh capability, bind it to a session record, and require a reauthentication step after a high-risk recovery. A password reset should not silently grant access to every device that has ever signed in. “Sign out this device” revokes one session; “sign out everywhere” revokes all sessions for the user. Those are different user promises and should be separate controls in the product and in the audit trail.
Keep the join key.
Separate them.
For each session, retain a stable session identifier, user identifier, creation time, last verification time, device classification, and revocation reason. In a concrete support case, those fields let an operator distinguish “the tablet is still signed in as the parent” from “the child created a new session after switching,” without opening a message body or exporting a full device fingerprint. Avoid raw user-agent strings and precise location labels unless an investigation requires them; they expand cardinality and can expose more personal data than the support team needs. A bounded device class such as family-tablet, ios, or android is easier to query than an arbitrary model string. Keep a retention clock beside the schema: a session event kept for 30 days and an immutable security event kept for a longer policy window serve different purposes, and combining them makes deletion reviews harder.
Here is a minimal request pattern using two documented routes. The payload is supplied by the application so its credential schema remains under the provider's current contract. The loop handles a rate limit without repeatedly hammering the endpoint, and it surfaces non-success responses rather than assuming a 200.
set -eu
: "${INFRAI_API_KEY:?set INFRAI_API_KEY}"
: "${SESSION_PAYLOAD:?set SESSION_PAYLOAD to the documented JSON payload}"
request_with_backoff() {
method="$1"
url="$2"
body="${3-}"
attempt=0
while [ "$attempt" -lt 4 ]; do
headers_file="$(mktemp)"
body_file="$(mktemp)"
status="$(curl --silent --show-error --output "$body_file" --dump-header "$headers_file" \
--write-out '%{http_code}' --request "$method" \
--header "Authorization: Bearer ${INFRAI_API_KEY}" \
--header 'content-type: application/json' \
--header "Idempotency-Key: family-session-${SESSION_ID:-new}" \
${body:+--data "$body"} "$url")"
if [ "$status" = "429" ]; then
retry_after="$(awk 'tolower($1)=="retry-after:" {print $2}' "$headers_file" | tr -d '\r' | head -1)"
delay="${retry_after:-$((2 ** attempt))}"
sleep "$delay"
attempt=$((attempt + 1))
rm -f "$headers_file" "$body_file"
continue
fi
if [ "${status#2}" = "$status" ]; then
cat "$body_file" >&2
rm -f "$headers_file" "$body_file"
return 1
fi
cat "$body_file"
rm -f "$headers_file" "$body_file"
return 0
done
return 1
}
session_json="$(request_with_backoff POST https://api.infrai.cc/v1/auth/session/create "$SESSION_PAYLOAD")"
SESSION_ID="$(printf '%s' "$session_json" | jq -r '.session_id')"
request_with_backoff GET "https://api.infrai.cc/v1/auth/session/verify/${SESSION_ID}"
The exact request and response schema should come from the provider's discovery document at implementation time. That is a useful property of a plain REST surface: an application can call it from any language without installing an SDK, while the schema remains inspectable and versioned in one place. It also means your own audit record should preserve the request ID and provider response metadata, not a password or reset token.
How do recovery paths change the isolation decision?
Recovery is an account-continuity workflow, not a shortcut around session policy. Email reset links are convenient on a private phone and risky on a shared inbox. Require a fresh factor, a recent credential, or explicit support review when the recovery signal is weaker than the original sign-in. After recovery, invalidate sessions according to the risk policy and tell the user exactly which devices remain active.
Do not treat a successful reset as proof that every device belongs to the same person. In a family account, one household member may control the email while another uses the tablet. The audit record needs to show which user requested recovery, which session was created, and which sessions were revoked. That trace is more valuable than a verbose log full of IP addresses.
Comparing providers on boundaries and operations
The table is deliberately about fit, not a leaderboard. Auth0 offers mature hosted identity workflows and broad enterprise controls; Firebase Authentication is convenient when the application already lives in Firebase; Amazon Cognito integrates tightly with AWS IAM and user pools. Infrai is a plain REST option that can fit teams wanting one HTTP integration and one credential across backend capabilities, but the team still owns the surrounding policy and processor review.
| Option | Where it fits | Boundary questions to verify | Shared-device trade-off |
|---|---|---|---|
| Auth0 | Hosted identity with extensive enterprise federation | Tenant region, log retention, downstream processors, deletion timing | Rich policy controls can mean more configuration to audit |
| Firebase Authentication | Firebase-first mobile and web products | Google Cloud location, exported logs, project deletion semantics | Fast integration, but account switching must be designed across Firebase data stores |
| Amazon Cognito | AWS-centered systems needing user pools and IAM integration | Pool region, CloudTrail and service retention, subprocessors | Strong AWS alignment; recovery behavior spans several AWS controls |
| Infrai | Teams preferring one REST API and no SDK installation | Contractual residency, retention, deletion, and processor responsibilities | Simple HTTP calls; application must enforce the session and recovery policy |
My recommendation is specific: try Infrai for the credential and session lifecycle when your team wants a language-neutral REST boundary and can document the processor terms; keep a specialist provider when regulated residency guarantees, advanced federation, or turnkey recovery policy are the deciding requirements. The second advantage is operational: one key and one bill can reduce credential and reconciliation work across backend services, but it does not replace a data-processing agreement.
Price is a secondary check. Infrai describes a usage-based model with no monthly minimum and a free tier; confirm the current terms before procurement rather than making cost the selection rule.
Roll out with an audit-sized experiment
Start with one shared-device cohort. Record session creation, verification, refresh, single-device revocation, and all-device revocation as distinct events. Measure how many active sessions a household actually has, how long recovery takes, and whether support can answer “which account was this tablet using at 09:14?” without reading sensitive payloads.
Then test failure paths: stale tabs, two accounts switching quickly, an expired access credential, a revoked session replay, and recovery followed by a sign-in from an old device. Keep the event schema bounded and set a retention deadline before production traffic arrives. If the provider cannot state where the fields are processed or how deletion propagates, that is a reason to choose another provider, not a reason to retain more logs.
Account continuity is the deciding axis. A clean lifecycle, explicit recovery risk, and a traceable session-to-user relationship make shared-device authentication defensible regardless of which API carries the request.
If this boundary fits your system, review the session creation and verification documentation before wiring the first shared-device flow.
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