# encodeBase64UrlToBase64

## `encodeBase64UrlToBase64` Function

The `encodeBase64UrlToBase64` function converts a **Base64URL-encoded string** back into a **standard Base64** format. This is useful for decoding or interoperability with systems that expect standard Base64 syntax.

***

### Purpose

Use this function when you need to:

* Convert a **Base64URL-safe string** into a **valid Base64 string**
* Decode values originally encoded in Base64URL (e.g., JWT segments)
* Restore compatibility with tools or APIs that do not accept Base64URL

> 🔗 Specification: [Base64URL Standard – base64.guru](https://base64.guru/standards/base64url)

***

### Function Definition

| Property          | Description                               |
| ----------------- | ----------------------------------------- |
| **Function Name** | `this.encodeBase64UrlToBase64`            |
| **Type**          | `function`                                |
| **Available In**  | Server-Side Variables                     |
| **Returns**       | `string` (Base64-standard encoded output) |

***

### Parameters

| Parameter | Description                      | Type     | Required                                      | Example     |
| --------- | -------------------------------- | -------- | --------------------------------------------- | ----------- |
| `input`   | A valid Base64URL-encoded string | `string` | <i class="fa-square-check">:square-check:</i> | `"YWJjKys"` |

***

### Conversion Behavior

This function performs the following transformations:

| Base64URL Character | Replaced With (Base64)                      |
| ------------------- | ------------------------------------------- |
| `-`                 | `+`                                         |
| `_`                 | `/`                                         |
| *(padding)*         | Adds `=` to match Base64 length (if needed) |

***

### Example Usage

```js
async function() {
    let x = this.encodeBase64UrlToBase64("YWJjKys"); // Base64URL of "abc++"
    return x; // → "YWJjKys="
}
```

This example converts a Base64URL-safe string into a valid Base64 string by restoring special characters and padding.

***

### Use Cases

* Decode JWT payloads or headers encoded in Base64URL
* Restore encoded values for Base64-compatible APIs
* Ensure data consistency across encoding formats

***

### Notes

* The input **must** be a valid Base64URL string.
* This function **does not decode** the value — it only **reformats** Base64URL to Base64. Use decoding functions separately if needed.
* Automatically restores padding (`=`) when missing.

***

### Summary

`this.encodeBase64UrlToBase64` enables seamless transformation of Base64URL-safe strings into **standard Base64** format. It ensures compatibility with systems expecting strict Base64 syntax, making it essential for working with JWTs, APIs, or external integrations in JENTIS.