fix: make login idempotent (#1149)

Logging with the same account several times creates and stores redundant
proofs and then sends them over during invocations.

Changes here avoid this redundancy by returning an account using
existing proofs if you already happen to have them, essentially making
login idempotent.

packages/w3up-client/src/account.js

@@ -80,6 +80,22 @@ export const list = ({ agent }, { account } = {}) => {
  */
 export const login = async ({ agent }, email) => {
   const account = fromEmail(email)
+
+  // If we already have a session for this account we
+  // skip the authentication process, otherwise we will
+  // end up adding more UCAN proofs and attestations to
+  // the store which we then will be sending when using
+  // this account.
+  // Note: This is not a robust solution as there may be
+  // reasons to re-authenticate e.g. previous session is
+  // no longer valid because it was revoked. But dropping
+  // revoked UCANs from store is something we should do
+  // anyway.
+  const session = list({ agent }, { account })[account]
+  if (session) {
+    return { ok: session }
+  }
+
   const result = await Access.request(
     { agent },
     {
@@ -140,6 +156,16 @@ export class Account {
     this.proofs.push(proof)
   }
 
+  toJSON() {
+    return {
+      id: this.did(),
+      proofs: this.proofs
+        // we sort proofs to get a deterministic JSON representation.
+        .sort((a, b) => a.cid.toString().localeCompare(b.cid.toString()))
+        .map((proof) => proof.toJSON()),
+    }
+  }
+
   /**
    * Provisions given `space` with this account.
    *

packages/w3up-client/test/account.test.js

@@ -67,6 +67,33 @@ export const testAccount = {
     assert.ok(two[Account.fromEmail(bobEmail)].toEmail(), bobEmail)
   },
 
+  'login idempotence': async (assert, { client, mail, grantAccess }) => {
+    const email = 'alice@web.mail'
+    const login = client.login(email)
+    await grantAccess(await mail.take())
+    const alice = await login
+
+    assert.deepEqual(
+      Object.keys(client.accounts()),
+      [alice.did()],
+      'no accounts have been saved'
+    )
+
+    const retry = await client.login(email)
+    assert.deepEqual(
+      alice.toJSON(),
+      retry.toJSON(),
+      'same account view is returned'
+    )
+
+    const loginResult = await Account.login(client, email)
+    assert.deepEqual(
+      alice.toJSON(),
+      loginResult.ok?.toJSON(),
+      'same account is returned with low level API'
+    )
+  },
+
   'client.login': async (assert, { client, mail, grantAccess }) => {
     const account = client.login('alice@web.mail')
 
@@ -217,8 +244,6 @@ export const testAccount = {
     const space = await client.createSpace('test')
     assert.deepEqual(client.spaces(), [])
 
-    console.log(space)
-
     const result = await space.save()
     assert.ok(result.ok)