JSON file for installing Rift Modloader in Minecraft 1.13.2 in MultiMC. Download Rift here: https://github.com/Chocohead/Rift

org.dimdev.rift.json

{
    "+tweakers": [
        "org.dimdev.riftloader.launch.RiftLoaderClientTweaker"
    ],
    "formatVersion": 1,
    "+libraries": [
        {
            "name": "com.github.Chocohead:Rift:jitpack-SNAPSHOT",
            "url": "https://www.jitpack.io/"
        },
        {
            "name": "org.dimdev:mixin:0.7.11-SNAPSHOT",
            "url": "https://www.dimdev.org/maven/"
        },
        {
            "name": "org.ow2.asm:asm:6.2",
            "url": "http://repo1.maven.org/maven2/"
        },
        {
            "name": "org.ow2.asm:asm-commons:6.2",
            "url": "http://repo1.maven.org/maven2/"
        },
        {
            "name": "org.ow2.asm:asm-tree:6.2",
            "url": "http://repo1.maven.org/maven2/"
        },
        {
            "name": "net.minecraft:launchwrapper:1.12"
        }
    ],
    "mainClass": "net.minecraft.launchwrapper.Launch",
    "name": "Rift",
    "releaseTime": "2018-07-18T15:11:46+00:00",
    "requires": [
        {
            "equals": "1.13.2",
            "uid": "net.minecraft"
        }
    ],
    "uid": "org.dimdev.rift",
    "version": "v1.0.4-77"
}

I used your json file for rift 1.13.2, but I'm getting this:

Instance update failed because: Game update failed: it was impossible to fetch the required libraries.
Reason:
Job 'Libraries for instance Rift 1.13.2' failed to process:
https://www.jitpack.io/INVALID

This is my json file after I edited yours: I have the libraries folder with = Rift-jitpack-1b46b5dcf4-1

{
"+tweakers": [
"org.dimdev.riftloader.launch.RiftLoaderClientTweaker"
],
"formatVersion": 1,
"+libraries": [
{
"name": "com.github.chocohead:rift-jitpack-1b46b5dcf4-1",
"url": "https://www.jitpack.io/"
},
{
"name": "org.dimdev:mixin:0.7.11-SNAPSHOT",
"url": "https://www.dimdev.org/maven/"
},
{
"name": "org.ow2.asm:asm:6.2",
"url": "http://repo1.maven.org/maven2/"
},
{
"name": "org.ow2.asm:asm-commons:6.2",
"url": "http://repo1.maven.org/maven2/"
},
{
"name": "org.ow2.asm:asm-tree:6.2",
"url": "http://repo1.maven.org/maven2/"
},
{
"name": "net.minecraft:launchwrapper:1.12"
}
],
"mainClass": "net.minecraft.launchwrapper.Launch",
"name": "Rift",
"releaseTime": "2018-07-18T15:11:46+00:00",
"requires": [
{
"equals": "1.13.2",
"uid": "net.minecraft"
}
],
"uid": "org.dimdev.rift",
"version": "v1.0.4-77"
}

You are have a dash (-) rather than a colon (:) after rift in the name field. Should be "name": "com.github.chocohead:rift:jitpack-1b46b5dcf4-1" . This is a common mistake to make as the file name and the format don't match.
I have updated the file to match the latest download.

I have updated the json file with a dynamic location for the rift loader com.github.Chocohead:Rift:jitpack-SNAPSHOT . It should continue to work across all new builds. At some point there may be a Release version and I will change it then.
If there are any problems please report on the YouTube video page https://youtu.be/y_4BlbBXEHI . I do not get notifications here.

ss

using https instead of http
http://repo1.maven.org/maven2/ -> https://repo1.maven.org/maven2/