Fix usage of non JSON numeric values for time fractions

The RFC-7519 states that the `NumericDate` type is:

> JSON numeric value representing the number of seconds from
> 1970-01-01T00:00:00Z UTC until the specified UTC date/time, ignoring
> leap seconds.

Then also mentions that time fractions (as covered by RFC-3339) are supported:

> Seconds Since the Epoch", in which each day is accounted for by
> exactly 86400 seconds, other than that non-integer values can be
> represented.

While adding support for time fractions we've interpreted the
"non-integer" really as any "non-integer" value, and used strings to
guard against precision issues.

That causes issues, since a string isn't a "JSON numeric value"
according to the JSON specs.

We observed that the 6-digit precision is not lost when doing JSON
encode/decode operations, this applies that technique to make sure we
comply to the specs and have "rounding issues" when dealing with floats.

src/Encoding/MicrosecondBasedDateConversion.php

@@ -25,16 +25,13 @@ public function formatClaims(array $claims): array
         return $claims;
     }
 
-    /** @return int|string */
+    /** @return int|float */
     private function convertDate(DateTimeImmutable $date)
     {
-        $seconds      = $date->format('U');
-        $microseconds = $date->format('u');
-
-        if ((int) $microseconds === 0) {
-            return (int) $seconds;
+        if ($date->format('u') === '000000') {
+            return (int) $date->format('U');
         }
 
-        return $seconds . '.' . $microseconds;
+        return (float) $date->format('U.u');
     }
 }

src/Token/Parser.php

@@ -12,8 +12,12 @@
 use function count;
 use function explode;
 use function is_array;
+use function is_string;
+use function json_encode;
 use function strpos;
 
+use const JSON_THROW_ON_ERROR;
+
 final class Parser implements ParserInterface
 {
     private Decoder $decoder;
@@ -105,7 +109,9 @@ private function parseClaims(string $data): array
                 continue;
             }
 
-            $claims[$claim] = $this->convertDate((string) $claims[$claim]);
+            $date = $claims[$claim];
+
+            $claims[$claim] = $this->convertDate(is_string($date) ? $date : json_encode($date, JSON_THROW_ON_ERROR));
         }
 
         return $claims;

test/unit/Encoding/ChainedFormatterTest.php

@@ -34,6 +34,6 @@ public function formatClaimsShouldApplyAllConfiguredFormatters(): void
         $formatted = $formatter->formatClaims($claims);
 
         self::assertSame('test', $formatted[RegisteredClaims::AUDIENCE]);
-        self::assertSame('1487285080.123456', $formatted[RegisteredClaims::EXPIRATION_TIME]);
+        self::assertSame(1487285080.123456, $formatted[RegisteredClaims::EXPIRATION_TIME]);
     }
 }

test/unit/Encoding/MicrosecondBasedDateConversionTest.php

@@ -36,8 +36,8 @@ public function dateClaimsHaveMicrosecondsOrSeconds(): void
         $formatted = $formatter->formatClaims($claims);
 
         self::assertSame(1487285080, $formatted[RegisteredClaims::ISSUED_AT]);
-        self::assertSame('1487285080.000123', $formatted[RegisteredClaims::NOT_BEFORE]);
-        self::assertSame('1487285080.123456', $formatted[RegisteredClaims::EXPIRATION_TIME]);
+        self::assertSame(1487285080.000123, $formatted[RegisteredClaims::NOT_BEFORE]);
+        self::assertSame(1487285080.123456, $formatted[RegisteredClaims::EXPIRATION_TIME]);
         self::assertSame('test', $formatted['testing']); // this should remain untouched
     }
 
@@ -62,7 +62,7 @@ public function notAllDateClaimsNeedToBeConfigured(): void
         $formatted = $formatter->formatClaims($claims);
 
         self::assertSame(1487285080, $formatted[RegisteredClaims::ISSUED_AT]);
-        self::assertSame('1487285080.123456', $formatted[RegisteredClaims::EXPIRATION_TIME]);
+        self::assertSame(1487285080.123456, $formatted[RegisteredClaims::EXPIRATION_TIME]);
         self::assertSame('test', $formatted['testing']); // this should remain untouched
     }
 }

test/unit/Token/ParserTest.php

@@ -453,7 +453,7 @@ public function parseMustConvertDateClaimsToObjects(): void
     {
         $data = [
             RegisteredClaims::ISSUED_AT => 1486930663,
-            RegisteredClaims::EXPIRATION_TIME => '1486930757.023055',
+            RegisteredClaims::EXPIRATION_TIME => 1486930757.023055,
         ];
 
         $this->decoder->expects(self::exactly(2))