Adjust behaviour of WithIssuedAt ParserOption (#411)

validator.go

@@ -112,11 +112,10 @@ func (v *Validator) Validate(claims Claims) error {
 		errs = append(errs, err)
 	}
 
-	// Check issued-at if the option is enabled
-	if v.verifyIat {
-		if err = v.verifyIssuedAt(claims, now, false); err != nil {
-			errs = append(errs, err)
-		}
+	// Check issued-at if the option is enabled, but usage of the claim
+	// itself is OPTIONAL.
+	if err = v.verifyIssuedAt(claims, now, v.verifyIat); err != nil {
+		errs = append(errs, err)
 	}
 
 	// If we have an expected audience, we also require the audience claim

validator_test.go

@@ -231,17 +231,23 @@ func Test_Validator_verifyIssuedAt(t *testing.T) {
 	}{
 		{
 			name:    "good claim without iat",
-			fields:  fields{verifyIat: true},
+			fields:  fields{verifyIat: false},
 			args:    args{claims: MapClaims{}, required: false},
 			wantErr: nil,
 		},
+		{
+			name:    "bad claim without iat",
+			fields:  fields{verifyIat: true},
+			args:    args{claims: MapClaims{}, required: true},
+			wantErr: ErrTokenRequiredClaimMissing,
+		},
 		{
 			name:   "good claim with iat",
 			fields: fields{verifyIat: true},
 			args: args{
 				claims:   RegisteredClaims{IssuedAt: NewNumericDate(time.Now())},
 				cmp:      time.Now().Add(10 * time.Minute),
-				required: false,
+				required: true,
 			},
 			wantErr: nil,
 		},