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The way I do it. Note there may be a more straightforward way.

Step 1

Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
}
add_filter( 'query_vars', 'my_custom_query_vars' );

Step 2

Add foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules[$key] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    }
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

Step 3

Hook into the parse_request filter to parse your request and redirect as necessary.

 function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['redirect_to']))){
        wp_redirect(home_url('/'.$wp->query_vars['redirect_to']));
        exit;        
}
add_action('parse_request', 'my_custom_parse_request');
    

The way I do it. Note there may be a more straightforward way.

Step 1

Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
}
add_filter( 'query_vars', 'my_custom_query_vars' );

Step 2

Add foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules['^'.$key.'$'] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    }
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

Step 3

Hook into the parse_request filter to parse your request and redirect as necessary.

 function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['redirect_to']))){
        wp_redirect(home_url('/'.$wp->query_vars['redirect_to']));
        exit;        
}
add_action('parse_request', 'my_custom_parse_request');
    

The way I do it. Note there may be a more straightforward way.

step 1: Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
}
add_filter( 'query_vars', 'my_custom_query_vars' );

step 2: a foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules[$key] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    }
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

step 3: hook into the parse_request filter to parse your request and redirect as necessary.

 function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['rediect_to']))){
        wp_redirect(home_url('/'.$wp->query_vars['rediect_to']));
        exit;        
}
add_action('parse_request', 'my_custom_parse_request');
    

The way I do it. Note there may be a more straightforward way.

Step 1

Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
}
add_filter( 'query_vars', 'my_custom_query_vars' );

Step 2

Add foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules[$key] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    }
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

Step 3

Hook into the parse_request filter to parse your request and redirect as necessary.

 function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['redirect_to']))){
        wp_redirect(home_url('/'.$wp->query_vars['redirect_to']));
        exit;        
}
add_action('parse_request', 'my_custom_parse_request');
    

The way I do it. Note there may be a more straightforward way.

step 1: Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
}
add_filter( 'query_vars', 'my_custom_query_vars' );

step 2: a foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules[$key] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    }
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

step 3: hook into the parse_request filter to parse your request and redirect as necessary.

 public function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['rediect_to']))){
        wp_redirect(home_url('/'.$wp->query_vars['rediect_to']));
        exit;        
}
add_action('parse_request', 'my_custom_parse_request');
    

The way I do it. Note there may be a more straightforward way.

step 1: Add a custom query_varlike this to record the redirect from/to variables

function my_custom_query_vars($vars){
     //this allows you to store custom variables with rediect_from and rediect_to in the url
     $vars[] = 'redirect_from';
     $vars[] = 'redirect_to';
    return $vars;
}
add_filter( 'query_vars', 'my_custom_query_vars' );

step 2: a foreach loop that does something like this. This will add the rewrite rules to change http://example.com/foo to http://example.com/?redirect_from=foo&redirect_to=bar

function my_custom_rewrite_rules($wp_rewrite){
    $new_rules = array();
    $json = '';//get your json data and store it as this string
    $json_array = json_decode($json, true);
    foreach($json_array as $key => $value){
        $new_rules[$key] = 'index.php/?redirect_from='.$key.'&redirect_to='.$value;
    }
    $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}
add_action('generate_rewrite_rules', 'my_custom_rewrite_rules');

step 3: hook into the parse_request filter to parse your request and redirect as necessary.

 function my_custom_parse_request($wp){
//we make sure the keys are present and not empty before we redirect
if ((array_key_exists('redirect_from', $wp->query_vars) 
    && !empty($wp->query_vars['redirect_from']))
    && (array_key_exists('redirect_to', $wp->query_vars)
    && !empty($wp->query_vars['rediect_to']))){
        wp_redirect(home_url('/'.$wp->query_vars['rediect_to']));
        exit;        
}
add_action('parse_request', 'my_custom_parse_request');